The basic problem is that trinitarianism is a non- scriptural doctrine that contradicts a number of biblical teachings and many specific verses of scripture. Also, the most obvious internal contradiction is how there can be three persons of God in any meaningful sense and yet there be only one God.
Here is compiled a number of other contradictions and problems associated with trinitarianism. Note: This list is not exhaustive but it does give an idea of how much the doctrine deviates from the Bible.
1. Did Jesus have two fathers? The father is the father of the son (1John1:3), yet the child born of Mary was conceived of the Holy Ghost Matt1:18,20; Luke1:35. Which one is the true father? Some Trinitarians claim that the Holy Ghost was merely the fathers agent in conception-a process they compare to artificial insemination!
2. How many spirits are there? God the father is a Spirit John4:24, the Lord Jesus is a Spirit 2Cor3:17 and the Holy Spirit is Spirit by definition. Yet there is one Spirit 1Cor12:13; Eph4:4
3. If Father and Son are co-equal persons, why did Jesus pray to the Father? Matt11:25. Can God pray to God?
4. Similarly, how can the Son not know as much as the Father? Matt24:36; Mark13:32.
5. Similarly, how can the Son not have any power except what the Father gives Him? John5:19,30; 6:38.
6. Similarly, what about other verses from scripture indicating the inequality of the Son and the Father? John8:42; 14:28; 1Cor11:3.
7. Did God the Son die? The Bible shows that the Son died Rom5:10. If so, can God die? Can part of God die?
8. How can there be an eternal Son when the Son was clearly begotten, indicating an obvious beginning John3:16; Heb1:5-6.
9. If the Son is eternal and existed at creation, who was His mother during that time? The Son was made of a woman Gal4:4.
10. Did God the Son surrender His omnipresence while on earth? If so, how could He still be God?
11. If the Son is eternal and immutable (unchanging), how can the reign of the Son have a ending? 1Cor15:24-28.
12. Whom do we worship and to whom do we pray? Jesus said to worship the Father John4:21-24, yet Stephen prayed to Jesus Acts7:59-60.
13. Can there be more than three persons in the Godhead? Obviously the OT does not teach three, but emphasizes the simple fact that there is only one.
14. Are there three Spirits in a Christians heart? Father, Jesus, and the Spirit all dwell within a Christian John14:17,23; Rom8:9; Eph3:14-17. Yet there is only one Spirit 1Cor12:13; Eph4:4.
15. There is only one throne in heaven Rev4:2. Who sits upon it? Jesus does Rev1:8,18; 4:8. Where do the Father and the Holy Spirit sit?
16. If Jesus is seated on the throne, how can He sit on the right hand of God? Mark16:19. Does He sit or stand on the right hand of God? Acts7:55. Or is He in the Fathers bosom? John1:18.
17. How is Jesus part of the Godhead, when clearly the Godhead is in Jesus? Col2:9.
18. Given Matt 28:19, why did the apostles consistently baptize both Jews and Gentiles using only the name of Jesus, even to the extent of rebaptism?Acts2:38; 8:16; 10:48; 19:5; 22:16; 1Cor1:13.
19. Who raised Jesus from the dead? Did the Father Eph1:20, or Jesus John2:19-21, or the Spirit? Rom8:11.
20. If the Son and Holy Ghost are co-equal persons in the Godhead, then why is blasphemy of the Holy Ghost unforgivable but blasphemy of the Son is not? Luke12:10.
21. If the Holy Ghost is a co-equal member of the trinity, why does the Bible always show the Him being sent from the Father or from Jesus? John14:26; 15:26.
22. If they are co-equal, why does the Holy Ghost not know what the Father knows regarding the return of Christ Mark13:32.
23. If the Spirit proceeds from the Father, is the Spirit also a son of the Father? If not, why not?
24. If the Spirit proceeds from the Son, is the Spirit the grandson of the Father? If not, why not?......................and so on
.and so on!
I believe that trinitarinism is not a biblical doctrine and that it plainly contradicts the Bible in many ways. Scripture does not teach a trinity of persons. Trinity doctrine uses terminology not used in scripture. It teaches and emphasizes plurality in the Godhead while the Bible emphasizes the fact that God is one and only one. It detracts from the fullness of Jesus Christs Deity. It contradicts many specific verses of scripture. It is not logical. It cannot be explained rationally, not even by those who advocate it.
I also find it strange to say to someone that God is One and yet three distinct persons that make up the One. How about this: Hear O Israel, I am three seperate persons that make me the One God.
And before anyone tries to post reasons for the trinity, I must let you know first: I was born into, raised up in, attended trinitarian college/bible school. I was where many of you are today!
I mean not to offend.