Islamic main teachings are teachings of antichrist according to Bible. Islam is biblical theology of antichrist. First, to be able to understand this, we must understand what antichrist is. It's true definition.
Islam also has concept of antichrist, but it is not authentic one. Islamic definition is caused by the influence of judeo-christian sects (which Muhammad encountered) and it is written in the hadiths, islamic sacred scriptures. First and only true authentic definition of antichrist comes from the Bible:
Bible says:
1 John 2, 22 Who is the liar? It is whoever denies that Jesus is the Christ. Such a person is the antichrist - denying the Father and the Son.
In islamic theology, main concept is to accept God, but to deny image of Father and Son in it. If you look closer to the quote in 1 John 2, 22, you will see that Bible perfectly prophesies teachings of islamic theology: it doesen't say about not believing in God. Quote contrary. Liar is not described as one who doesen't accpet one God (Jews, christians, muslims all believe in one God), but it only denies Father and Son it it's image. And that is what islam teaches. It is described and applied in perfection.
Some may agrue - it says also: "whoever denies that Jesus is the Christ...", and islam in it's way doesen't deny Jesus is Christ. That is true (we won't go in detail to differences for what Jesus being Christ means in christianity, and what in islam), but definition carries more statements. Certianly those who deny Jesus is Christ (for example, pagans, hebrews, non believers) are ones that words may refere to. But there also we have special group of people who deny precisely Father and Son. And if they deny both of them, they are prophesied in perfection. And that kind of teaching perfectly carries islam. In Bible, Old Testament, Jews also know the concept of God as the Father. God is decribed as Father in both Old Testament and New Testament, in many passages. So this denial case "denying the Father and the Son" can be applied only in half way to Jews, as they only reject Son. But muslims, they reject both Father and Son. As, according to Quran, God cannot have Son, and Allah is not the Father. So islam is prophesied in the Bible, but unlike what our muslim friends tell us (their misconceptions about Muhammad being prophesied in the Bible although Bible clearly said Conforter (that is, Holy Spirit), came already at the time of first christians as New Testament describes us).
More confirmations that islam is prophesised as antichrist teaching are also in the Bible. Look carefully at these sentences:
Galatians 1, 8 But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let them be under God’s curse! 9 As we have already said, so now I say again: If anybody is preaching to you a gospel other than what you accepted, let them be under God’s curse!
As you can see, here author multiple times explicitly expresses great danger. Here, it is descibed that if angel would came and preach a gospel to someone and if it would be different than one we have (that there is only One God, and it is in image of Father and Son, and it is revealed in Father Son and Holy Spirit), that it would be evil angel. And what happened 600 years later? Angel Jibreel came, to said Muhammed: this Quran is word of God, God is one, but you must deny Father and Son.
So, this was brief explanation why islamic theology is biblical theology of antichrist. Islam is prophesised in the Bible. But in a negative, demonic way. But it is not some book which was written after revelation of Quran where these claims are - it is Holy Bible where these facts are, centuries before Quran was revealed.
God bless you, and may Lord Jesus open your eyes.