Peace be upon you,
Your friend claimed that he left Islam for Christianity because of his understanding of Isaiah (35:4-6) which says about the coming of Jesus in God on earth.
• Isaiah (35:4) say to those with fearful hearts, “Be strong, do not fear; your God will come, he will come with vengeance; with divine retribution he will come to save you.”
Please note that the verse says "your God" “your God will come, he will come with vengeance…” but it does not say that God will come in the shape of a man. God’s knowledge is everywhere and He can send His revenge to the wicked and save the righteous from anywhere. It simply means that God will come to punish and save from anywhere and anytime but NOT as a man because He clearly said that He is not a man.
• Hosea (11:9) I will not execute the fierceness of mine anger, I will not return to destroy Ephraim: for I am God, and not man; the Holy One in the midst of thee: and I will not enter into the city.
• Numbers (23:19) God is not a man, that he should lie; neither the son of man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good?
Also, please note that Jesus is the son of mankind "Mary" and God said that He is neither a son of man nor a man, therefore, the addition that your friend has added to Isaiah (35:4) that the coming of God will be in Jesus on earth is completely false because Jesus said that he is a man.
• Acts (2:22) “Men of Israel, hear these words! Jesus of Nazareth, a man approved by God to you by mighty works and wonders and signs which God did by him in the midst of you, even as you yourselves know,
Next, I did not understand why your friend understands from Matthew (11:3-5) that Jesus is god. These verses did not say that Jesus is god, it simply says that the blind will receive sight…the dead are raised… That’s exactly what God said in Quran, it says that Jesus will bring dead people to life BUT by the permission of God.
• Matthew (11:3) to ask him, “Are you the one who is to come, or should we expect someone else?” 4 Jesus replied, “Go back and report to John what you hear and see: 5 The blind receive sight, the lame walk, those who have leprosy are cleansed, the deaf hear, the dead are raised, and the good news is proclaimed to the poor. 6 Blessed is anyone who does not stumble on account of me.”
• Quran (3:49) And [make him] a messenger to the Children of Israel, [who will say], 'Indeed I have come to you with a sign from your Lord in that I design for you from clay [that which is] like the form of a bird, then I breathe into it and it becomes a bird by permission of Allah. And I cure the blind and the leper, and I give life to the dead - by permission of Allah. And I inform you of what you eat and what you store in your houses. Indeed in that is a sign for you, if you are believers.
God said in Deuteronomy (13:1-5) not to listen to any prophet who asks you to worship other gods. But Prophet Mohamed (PBUH) asked us to worship God which Prophet Abraham, Moses, Jesus, Jacob, etc. worshipped. Please note that verse 5 says that a false prophet must be put to death. But God did not allow anyone to kill Prophet Mohamed (PBUH). He remained alive for 22 years until he delivered Quran to mankind. Also, keep in mind that Prophet Mohamed (PBUH) was engaged in many battles, yet God protected him.
• Deuteronomy (13:5) That prophet or dreamer must be put to death for inciting rebellion against the Lord your God, who brought you out of Egypt and redeemed you from the land of slavery. That prophet or dreamer tried to turn you from the way the Lord your God commanded you to follow. You must purge the evil from among you.
Please note that the verse says that “That prophet or dreamer tried to turn you from the way the Lord your God commanded you to follow”, but Prophet Mohamed (PBUH) did not turn us from the way of God. In fact, he brought us very close to God because he forbid adultery, murdering an innocent person for no reason, robbery, and so on and he asked us to help each other and help the needy ones and so on.
Regarding Psaume (3:3), you said that David is the one who calls God and not the other way around. This is correct. Then you said that we also see that David does not have his own glory because the only glory he has is that of God which is therefore not his. This is correct, no one has glory other than God, not even Prophet Mohamed or Jesus or any other Prophet. You also said that the Father “God” did not give glory to men. This is also correct because God said in Isaiah He does not share His glory with anyone.
• Isaiah (42:8) I am the Lord; that is my name; my glory I give to no other, nor my praise to carved idols
And for Psaume (8:5) you said that it is men who were speaking to God about Jesus! No, it is David who was glorifying God and acknowledging His favors on mankind.
Regarding verse John (17:24) which says that God gave His glory to Jesus is modified and false because it contradicts Isaiah (42:8) which says God does not give His glory to no other. The meaning of “no other” is to NONE including Jesus and Mohamed and the greatest angels.
• John (17:24) “Father, I want those you have given me to be with me where I am, and to see my glory, the glory you have given me because you loved me before the creation of the world.
My advice to your friend and other Muslims who are leaving Islam because today Muslims are weak is to read the following verses from Quran and Isaiah. God said in Isaiah that He will deliver the Book to the illiterate man. Then God continued and said that He will destroy the people with many miracles because we will be worshipping Him in our mouths and lips, not in our hearts. So, please tell your friends who are leaving Islam and all Muslims to go back to the Book of Allah Quran and you will see the satisfactory results from God. According to Quran, Prophet Mohamed was illiterate.
• Quran (7:157) Those who follow the Messenger, the unlettered prophet, whom they find written in what they have of the Torah and the Gospel, who enjoins upon them what is right and forbids them what is wrong and makes lawful for them the good things and prohibits for them the evil and relieves them of their burden and the shackles which were upon them. So they who have believed in him, honored him, supported him and followed the light which was sent down with him - it is those who will be the successful.
• Isaiah (29:12-14) Then the book shall be delivered to him who is not learned, saying, “Read this, please.” And he shall say, “I cannot read.” 13 Therefore, the Lord said: Because this people draw near with their mouths and honor Me with their lips, but have removed their hearts far from Me, and their fear toward Me is tradition by the precept of men, 14 therefore I will once again do a marvelous work among this people, even a marvelous work and a wonder; for the wisdom of their wise men shall perish, and the understanding of their prudent men shall be hidden.
I hope this answers your questions, but if you still have more questions, please feel free to ask.
Regards,