"And this is eternal life, that they may know thee the only true God, and Jesus Christ, whom thou hast sent," (cf. John 17:4).
"... For if you believe not that I am he, you shall die in your sins," (cf. John 8:24).
"... For unless you believe I AM who I claim to be, you will die in your sins," (John 8:24, NLT).
"Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God," (cf. 2 John 9).
"Who do you say that I Am?" This is the whole point of Jesus and our faith, the one litmus test in our creed, to know Jesus, and what distinguishes us from false religions, sects, cults, and heresies. Remember: It's not how big your faith (but how big your God) nor how sincere or fanatical you are, but the object of your faith that saves; faith doesn't save, Jesus does--and it needs to be the real Jesus, the only begotten Son of God (coequal, coexistent, and coeternal to the Father).
When Jesus claimed to be God without even beating around the bush or using figurative language, only the Pharisees knew His claim and they plotted to kill Him for His "blasphemy." The disciple were clueless till the resurrection. The point is that you must believe in the real Jesus, who He claimed to be, and not just who you think He is or want Him to be. He was not God's surrogate or a deified man that was misunderstood by His disciples. They were not expecting the one they saw, for He was not the Messiah of conventional wisdom and that they were taught (a mighty conquer who would liberate Israel from Rome).
Jesus was who He claimed to be or He is a demon, liar, or even lunatic (and there is no evidence to lend credence to any of these false beliefs) because He clearly claimed deity. It was only because of preconceived notions and ignorance of prophecy that they couldn't see the truth. Jesus did fulfill over 333 prophecies to the letter. The Jews you will know were monotheistic and couldn't conceive of a triune Godhead. Jesus was truly man as well as truly God and they only saw His humanity and that He was a man but didn't see that He is One with the Father. He demonstrated and proved His divine claim by the ultimate and final evidence of the resurrection, which Luke said had "many infallible proofs."
They may have seen Him as a Son of God, even calling Him "Lord" and worshiping Him, but not God made man--God with skin on or personified in the flesh. But it is only because He is God that He's fully adequate and qualified to be our Savior! He can suffer the infinite penalty and price for sin on our behalf. This is theologically called the atonement and Jesus death is substitutionary. He took on our sins so we would need not punishment. The principle of representation goes back to Adam who took our place as the head of the human race and sinned thus making us all sinners because of his one sin.
If a so-called Christian who claims to believe in Jesus receives Him without His claims to deity, they are denying Him and do not know the real Jesus but "another Jesus" (cf. 2 Cor. 11:4). The book of 2 John v. 9 says that if we do not abide in the doctrine of Christ we do not have the Father, meaning this is the litmus test for Christians--they know Jesus for who He is, not some deified man, demigod, or humanized God or man with superhuman powers.
But we must recognize that Jesus had to be God because it fulfilled the prophecies. The Jews were blinded to the truth and needed to be enlightened. Since He is the Almighty and our Creator, we must worship Him and surrender to Him our lives. In application, the Jehovah's Witnesses and the LDS do not have the right to go by the moniker Christian for they deny Jesus full Deity inclusion in the Godhead as coequal and coeternal to the Father. These belief systems are not bona fide denominations but sects. The only reason they really are not cults is that they don't steal your money and have slaves and people who don't know how to escape like the Church of Scientology. But LDS are erroneous in claiming secret knowledge and this was the error of the Gnostics who believed in salvation via secret knowledge or enlightenment.
Sooner or later all of us must come to the decision of whether we will accept the Jesus He claimed to be: Lord of all! But we cannot come to Jesus on our own initiative; the Father must woo or draw us to Him--the call must be granted by the Father. "As many as were appointed to eternal life believed," (cf. Acts 13;48). Paul said in Rom. 11:7 that the elect obtained unto it and the rest were blinded or hardened--God must open the eyes of our hearts and kindle faith. It literally takes a miracle to change someone's heart and open it to receive the Lord. The general call of the gospel goes out to all (cf. Titus 2:11) but whomever God calls always gets saved (cf. Rom. 8:29-30). "You did not choose Me, but I chose you," (cf John 15:16). That's why it's said, "Many are called but few are chosen," (cf. Matt. 22:14). Soli Deo Gloria!