Having an errant Christology leads to all sorts of weird doctrines.
Monophysites: believe Jesus had only one nature: divine. It is an error concerning the nature of Christ that asserts Jesus had only one nature & not two as is taught in the correct doctrine of the hypostatic union: Jesus is both God & Man in one person. In monophysitism, the single nature was divine & NOT human. It is sometimes referred to as Eutychianism, after Eutyches 378-452AD; but there are slight differences. Monophysitism arose out of a reaction against Nestorianism which taught Jesus was two distinct persons instead of one Person. Its roots can even be traced back to Apollinarianism which taught that the divine nature of Christ overtook & replaced the human one.
Monophysitism was confined mainly to the Eastern church & had little influence in the West. In 451, the Council of Chalcedon attempted to establish a common ground between the monophysitists & the orthodox, but it did not work and divisions arose in the Eastern church which eventually excommunicated the monophysitists in the 6th century. It was condemned as heresy at the 6th Ecumenical Council in 680-681.
The denial of the human nature of Christ is a denial of the true incarnation of the Word as a man. Without a true incarnation there can be no atonement of sin for mankind since it was not then a true man who died for our sins. It is a vital Christian doctrine & this is a serious heretical teaching.
Monothelites: (7th Century) This heresy emerged in response to the Monophysite heresy (see above), but it also taught something denied by the Scripture. The name is derived from a Greek root that means “one will”. Monothelitism taught Jesus had two natures but only one will.
Monothelitism – What is it?
Monothelitism is the teaching that Jesus has two natures but only one will. It was a teaching that began in Armenia and Syria in about 629 and remained popular among some until the Third Council of Constantinople at which it was officially condemned, with the church affirming dyothelitism (that Jesus has two natures and both a divine and human will).
This teaching falls within the larger theological area of study called Christology that deals with the person and nature of Jesus Christ. The Bible teaches that Jesus was human just like any other person, yet lived without sin (Hebrews 4:15). In addition, Jesus was often noted as divine and as eternal God (John 1:1). The question at that time was in how to understand this dual nature of Jesus (known as the hypostatic union). Did Jesus have only one will or did He have two wills, both a divine and human will?
The view of monothelitism held a compromise position that Jesus had two natures but only one will. This was in contrast with both the view that Jesus had only one nature (either human or divine) and that Jesus had two natures and two wills (dyothelitism).
Biblically, it can be shown that Jesus held both a human and divine nature, affirming dyothelitism and denying monothelitism. For example, in Luke 22:42 Jesus prayed to the Father, "Father, if you are willing, remove this cup from me. Nevertheless, not my will, but yours, be done." Jesus had a human will that desired not to die. He also had a divine will that was the same as the divine will of God the Father that would lead Him to die on the cross for humanity's sins.
Another example can be found in John 6:38 that reads, "For I have come down from heaven, not to do my own will but the will of him who sent me." The human desires of Jesus faced temptation as other people did (Matthew 4:1-10), yet He acknowledged His divine will to accomplish the work of God the Father.
Again, in John 10:17-18 we find, "For this reason the Father loves me, because I lay down my life that I may take it up again. No one takes it from me, but I lay it down of my own accord. I have authority to lay it down, and I have authority to take it up again. This charge I have received from my Father." Jesus had the same divine will as the Father, yet He also had to deal with His human will that did not desire to face suffering and death.
The Bible is clear that Jesus is both fully human and fully God, including both a divine and human will. Any view that some way makes Jesus less human or less divine stands in contrast with His revelations as God in human form (John 1:1; 14).
What is monothelitism?
To conclude, is the teaching of monothelitism biblical? There are numerous texts which could be cited to definitively prove that Christ possessed both a divine and a human will. In Hebrews 10:7, Paul applies to Christ the words of Psalm 40:7-8 – “Then I said, ‘Here I am, I have come – it is written about me in the scroll. I desire to do your will, O my God; your law is within my heart.’” Here, both wills are distinctly marked—the divine (“I desire to do your will, O my God”) and the human will, subject to the divine will (“your law is within my heart”).
Christ Himself draws the same distinction in many places. For example, in John 6:38, Jesus declares, “I have come down from heaven not to do my will but to do the will of him who sent me.” In Matthew, Christ says, “My father, if it is possible, may this cup be taken from me. Yet not as I will, but as you will.” And as Jesus declares in John 10:17-18, “The reason my Father loves me is that I lay down my life – only to take it up again. No one takes it from me, but I lay it down of my own accord. I have authority to lay it down and authority to take it up again. This command I received from my Father.” Clearly, these texts show the divine will which Christ had, in common with the Father and, in contrast, the human will which He subjected to the will of His Father.
Monoenergetics: Christ, though existing in two natures, had one energy (divine & human).
This is shown to be false in Scripture in that Christ could become tired in his human energy (John 4:6) yet God in His divine energy does not become tired, in a physical or human sense. (Isaiah 40:28).
The Third Council of Constantinople, counted as the Sixth Ecumenical Council[1] by the Eastern Orthodox and Catholic Churches, as well by certain other Western Churches, met in 680/681 and condemned monoenergism and monothelitism as heretical & defined Jesus Christ as having two energies & two wills (divine & human).
Heresy | CARM.org
Heresy is a false teaching. It is a belief or idea that is in contradiction to orthodoxy. In the context of Christianity, heresy is that which deviates from standard biblical teaching. Examples of heresy would be polytheism, a denial of the resurrection of Christ, a teaching that salvation is obtained by works, etc. The Christian church has experienced many attacks by heretics throughout the centuries, but it has fought them successfully.
"Error, indeed, is never set forth in its naked deformity, lest, being thus exposed, it should at once be detected. But it is craftily decked out in on attractive dress, so as, by its outward form, to make it appear to the inexperienced (ridiculous as the expression may seem) more true than truth itself," (Early 2nd century Church Father, Irenaeus Against Heresies 1.2).
The word "heresy" comes from the Greek 'hairesis' which means "choosing" or "faction." At first, the term heresy did not carry the negative meaning it does now. But, as the early church grew in its scope and influence throughout the Mediterranean area, various teachers proposed controversial ideas about Christ, God, salvation, and other biblical themes. It became necessary for the church to determine what was and was not true according to the Bible. For example, Arius of Alexandar (A.D. 320 ) taught that Jesus was a creation. Was this true? Was this important? Other errors arose. The Docetists taught that Jesus wasn't human. The Modalists denied the Trinity. The Gnostics denied the incarnation of Christ. Out of necessity, the church was forced to deal with these heresies by proclaiming orthodoxy; and in so doing, condemnation upon these heresies and the heretics became a reality.
Culturally, when Christianity arose, it arose in the midst of a hostile environment. Judaism and the Roman Empire both warred against its people and its teaching. Persecutions arose and Christians were killed for their faith. In the Diaspora (dispersion) of the late first century, Christians were scattered throughout the Mediterranean area due to the persecutions in Israel. The Roman Empire with its theology of many gods was not friendly to Christianity's monotheism. Therefore, Christians were further persecuted.
Theologically, the Bible teaches condemnation upon false doctrines and false teachers. Gal. 1:8-9 says, "But even though we, or an angel from heaven, should preach to you a gospel contrary to that which we have preached to you, let him be accursed. 9 As we have said before, so I say again now, if any man is preaching to you a gospel contrary to that which you received, let him be accursed." (See also 1 Cor. 16:22; 2 Cor. 11:13-15; 1 Tim. 1:18-20; Titus 3:10) Why is this taught in the Bible? The reason is simple. Christians are saved by faith in the work of Jesus on the cross, but faith in itself is not enough. Faith is not a substance you can put in a jar. It is belief in something. Faith is only as good as who it is placed in. If you put your faith in a false God, you are lost because a false god cannot save anyone. This is why God says in Exodus 20:3, "You shall have no other gods before Me." Faith is not what saves, but faith in the true God is what saves.
It becomes necessary to define those doctrines which separate Christian from non-Christian. It would make no sense to persecute anyone over a doctrine that is not essential to the faith. Such nonessentials, in my opinion, would include baptism of infants, pre- or post-trib rapture, worship on Saturday or Sunday, musical instruments in the church, the charismatic gifts, worship styles, dress codes, etc. These kinds of subjects do not affect one's salvation. Unfortunately, the disagreements that arise around these subjects result in denominational fragmentation.
Essentials of the faith would include who God is, who Jesus is, salvation by grace, and Jesus' resurrection. From these subjects we have derived doctrines known as the Trinity and the hypostatic union (Jesus' two natures: God and man). The Bible tells us that these doctrines concerning God, Christ, salvation, and resurrection are essential to the faith. Therefore, it is of the utmost importance that Christians know their faith and know how to defend it against the doctrines that compromise the essentials.
The list of heresies in this section represents serious assaults upon the character of God, of Christ, and of salvation itself. The church through the centuries as defined, let me correct myself, has recognized what the truth is concerning the essentials of the faith.
Heresies
Adoptionism - God granted Jesus powers and then adopted him as a Son.
Albigenses - Reincarnation and two gods: one good and other evil.
Apollinarianism - Jesus' divine will overshadowed and replaced the human.
Arianism - Jesus was a lesser, created being.
Docetism - Jesus was divine but only seemed to be human.
Donatism - Validity of sacraments depends on character of the minister.
Eutychianism - Jesus finite human nature is swallowed up in His infinite divine nature.
Gnosticism - Dualism of good and bad and special knowledge for salvation.
Kenosis - Jesus gave up some divine attributes while on earth.
Marcionism - An evil God of the O.T., good God of the N.T. 11, books in the Canon
Modalism - God is one person in three modes.
Monarchianism - God is one person.
Monophysitism - Jesus had only one nature: divine.
Nestorianism - Jesus was two persons.
Patripassionism - The Father suffered on the cross.
Pelagianism - Man is unaffected by the fall and can keep all of God's laws.
Semi-Pelagianism - Man and God cooperate to achieve man's salvation.
Socinianism - Denial of the Trinity. Jesus is a deified man.
Subordinationism - The Son is lesser than the Father in essence and or attributes.
Tritheism - The Trinity is really three separate gods.