It is very often stated by well-meaning people who want to bring all religions together, that we should focus on what we agree on, and stop majoring on the minors. It assumes the disagreements are petty and not worth getting concerned about.
It reminds me of a conversation I had with a Muslim gentleman named Mia (at least that's how it sounded, even if it's not how it's spelt). He was a lovely man, although I'm not sure he could be considered a very good Muslim based on the conversation we had. He came to hear me preach the Gospel quite a number of times, and one evening we had a discussion about it.
He told me that as a Muslim he believed in Christ, but I pointed out that what he meant when he spoke of believing in Christ was entirely different to what the Bible means when it speaks of believing in Christ. When the Bible speaks about believing in Christ it means trusting Him to save you from your sins and their penalty, it is depending on Him to do for you what you can't do for yourself, i.e. bring you into a right relationship with God. Believing in Christ is the opposite to a works-based system (one in which acceptance with God depends in whole or in part on your performance), see for example Ephesians 2 v 8, 9; Romans 3 v 21 - 4 v 8; Acts 13 v 38, 39. He agreed that he certainly didn't believe in Christ in the same way, that is he was not relying on Christ alone to save him from God's wrath against his sins.
I also pointed out to Mia that the Christ he "believed in" was different to the Christ presented in the Bible, because Mia did not believe that Christ was the eternal Son of God, Creator of all things, possessed of all the attributes of God. He agreed that this was indeed a difference between us.
We agreed on another disagreement! Mia didn't believe that Christ died on the cross. He then said to me that these are two things we disagreed on, but "they are minor differences" he said! I had to politely but firmly disagree! I told him that these were major differences. I think most Muslims would agree. For Muslims, the idea that Jesus is the Son of God is the ultimate blasphemy, while for Christians the idea that He's not the Son of God is the ultimate blasphemy! I told him that these two issues are so huge because if Jesus Christ were not the Son of God then He could not pay the penalty for our sins, and if He had not died then He did not pay the penalty for our sins.
Maybe these two issues need to be explained and expanded. Why is it essential that Jesus was the Son of God if He was to be able to pay the penalty for sin? This question takes me back to a chat I had with a man at an open air Gospel meeting a few years ago. The man began shouting at the preacher in quite an aggressive way, I summoned my courage (he was a big guy) and approached him - he turned out to be really good to talk to. He asked me this question, Jesus suffered for a few hours on the cross to save us from eternity in hell, why can't I just get all my suffering concentrated into a few hours instead of spread out over eternity? The answer to that question is because Jesus is the Son of God. Because God is infinitely holy and righteous then the penalty for sinning against Him is infinite. That's why, for finite creatures like us, the punishment is eternal - we can never exhaust it. Indeed, even the devil and the angels that sinned will suffer eternal punishment (Matthew 25 v 41; Revelation 20 v 10; Jude v 6) - those beings, though mighty, are finite and not able to pay the penalty that is demanded for their sin. That is why our salvation demanded the sacrifice of the infinite, almighty, uncreated Son of God. He was able to fully pay that penalty and fully exhaust that punishment. Such is the infinite worth of His Person that when He entered into God's judgment it was a payment of infinite value, such that, because of it all can be saved, but without it none could be saved. The Deity of Christ is therefore not some minor point of doctrinal debate.
But why was His death on the cross essential? After all, the sinner who dies without salvation isn't going to be crucified for his sins, so why did He have to be crucified? Well, the point is this, that the act of crucifying Christ did not provide salvation. The thorns on His brow, the nails in His hands and feet and the spear in His side didn't pay for sin, after all, those actions were sinful in themselves. Something much deeper and far greater happened at Calvary, because it was when the Lord was on the cross that the God laid on Him the iniquity of us all, and He bore the punishment for sin, not from the hands of men, but from the hand of God (Isaiah 53 v 5, 6, 10; 1Peter 2 v 24; 2Corinthians 5 v 21). The crucifixion of Christ showed the wickedness of man's heart, and meant that they were truly guilty of His murder - they passed the death sentence upon Him, but it was the bearing of God's wrath against sin that makes salvation available.
I hope Mia realises that these are the major issues. If He's not Divine He's not a Saviour, and if He never died He can never save. This is why the Lord said, "if you do not believe that I am He, you will die in your sins" (John 8 v 24)
