@MuslimView (argument/question not quoted) When God becomes Man, He prays as Man. But remaining God, He also shares the Majesty of the Father.
I have assumed your questions are honest, I have given straight answers, starting to comment from n 10 so n 9 came above it. If you click "show all comments" they will show in the right order and you can easily read them and ask follow up questions that will show between my answers.
1) Why does the Catholic Bible contain 73 books while the Protestant Bible has only 66?
- The Jews were the people of God, but were not yet united which books belonged to His word, if some of the older or the newest belonged to it or not. Christ came. Christians accepted the fuller version, in Greek, the Septuagint. That is why Catholics have 73 books, Orthodox 75. Jews rejected the Septuagint after rejecting Christ (at Jamnia, CE80). Protestants followed their version because it was in Hebrew. The Protestant major confessions - Lutherans, Calvinists, Anglicans - started 1500 years after Christianity, by men who were rejecting the Latin Translation of the Greek New Testament. Then they rejected the Latin translation of the Hebrew Old Testament too, but also the Greek Translation called the Septuagint. Also, these men rebelled against the Catholic Church on accounts where the books they rejected - notably Maccabees II, last book of Catholic Bible, supported Catholic practise.
2) Why do Christians say that God is three-in-one and one in three when Jesus says in Mark 12:29: "The Lord our God is one Lord"?
- Because the Three Persons are not three lords, but only One Lord. As already said by St Athanasius and by the First Council of Toledo, before your prophet was even around.
3) Why does the Bible say that Jesus wanted to die on the cross, when the one on the cross was shouting "My God, my God, why have you forsaken me?" according to Matthew 27:45 and Mark 15:33 ?
4) To whom did God lose Jesus if he owns the whole universe?
- God did not lose Jesus.
5) Why did Jesus should have been punished for sins that he didnt commit?
- If a foolish man incurs a debt, can no one else pay it for him?
6) Why we should be punished for the first sin that was commited by Adam?
- When a man doing evil is punished by forfeiting property, are not his children poorer too? If he forfeits liberty, are not his children born in bondage?
7) If all the Christians are saved through Jesus and are going to Heaven no matter what they do, then whats the point of the teachings of Jesus? and where does the importance of good and evil consists in?
- Not all Christians are saved. Those who hear Christ's words but do not do them as works are not saved.
8) How can Christians take deeds as irrelevant after becoming one when Jesus says in Matthew 12:36; "But I say unto you that every idle word that men shall speak, they shall give account thereof in the Day of Judgment. For by the words thou shalt be justified, and by the words thou shalt be condemned"?
- Deeds are not irrelevant. We need to pray, fast, give alms, abstain from sin as far as we can, get sins forgiven. You understood this right, some Protestants understood this wrong.
9) How did Jesus create his mother and she who gave birth to him.?
- Not in His Manhood, which He got from Her, but in His Divinity which from all Eternity He got from the Father. And the Son was not alone, but the Father and the Holy Ghost also created - both the world, and Heaven above, and the angels, and Mary, who was to be the Queen of all Angels.
10) why did God become human?
- To make us partakers of God's own life. Also, that God alone being perfect, He should perfectly repair for the Sins against the Perfect.