The Bible is extremely clear about how one is saved. The only "complication" is when extra-Biblical assertions, which are contrary to Scripture, are believed, or consequences in Scripture are believed to be causes.
Now that we have forgotten what "believe" means, it must be explained, but not defined in a hard and fast way, because it must use words that people understand differently. It does not mean intellectual assent, attending any church, having Christian parents, or any form of "going through the motions of any aspect of Christianity," and does not mean anything a person can choose or reject to do, including being baptized or taking communion. (The latter are signs that a person has chosen to be obedient to God.)
What "believe" does mean is genuinely believing that the Lord God Jesus Christ is real, He died for us, and was raised from the dead (for one's own benefit, I would add, accept Him as "my" God and believe all He said). Given a proper understanding of what believing is, this verse is an accurate description of what it takes to be saved:
“For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. (John 3:16, 1984 NIV)
Plenty of others:
That if you confess with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved. (Romans 10:9-10, 1984 NIV) (The confession, along with thankfulness, et al., must come from the heart.)
and this water symbolizes baptism that now saves you also—not the removal of dirt from the body but the pledge of a good conscience toward God. It saves you by the resurrection of Jesus Christ, (1 Peter 3:21, 1984 NIV) (... which also, btw, explains what the baptism is that saves—a response to God of commitment of a good conscience to Him.)
Therefore he is able to save completely those who come to God through him, because he always lives to intercede for them. (Hebrews 7:25, 1984 NIV)
I am extremely sick of hearing how some organized body of believers is necessary for a person to be saved. Who is it that died for you? Who is it that is must be your Lord? Who is it that knows how to rearrange a person's (spiritual) atoms so they are no longer condemned?
Is Christ divided? Was Paul crucified for you? Were you baptized into the name of Paul? (1 Corinthians 1:13, 1984 NIV)
For it is by grace you have been saved, through faith—and this not from yourselves, it is the gift of God—not by works, so that no one can boast. (Ephesians 2:8-9, 1984 NIV)
Anyone that thinks they must partially depend on anything or anyone in the physical realm for salvation, believes that Jesus Christ is not sufficient for salvation. If anyone teaches something other than salvation is by God's grace through faith that only God gives, then they have something "special" knowledge to "boast" about which proves they have rejected this verse as Truth. And they are in danger of fulfilling Matthew 7:15-23 or Matthew 18:6-7. If you are in the fellowship of those who teach things contrary to the Bible, then cut them off and move on. Jesus Christ is all you need for eternal life. Commit forever to Him from your heart and you are saved.
If your hand or your foot causes you to sin cut it off and throw it away. It is better for you to enter life maimed or crippled than to have two hands or two feet and be thrown into eternal fire. And if your eye causes you to sin, gouge it out and throw it away. It is better for you to enter life with one eye than to have two eyes and be thrown into the fire of hell. (Matthew 18:8-9, 1984 NIV)
What God has commanded and entrusted to people that call themselves by His name is to tell people about Jesus, and make those who believe that Good News into disciples of Jesus. Trying to exert more power over people than that is manipulation, which is at its heart, the sin of witchcraft (trying to exert supernatural power).
For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven. (Matthew 5:20, 1984 NIV)