If you came to a Christian and said to him: " Jesus is Muslim".
He may stare at you and say: " Are you kidding me? How do you say that Jesus is Muslim?!! Jesus is actually a Jew who came 600 years before Islam.
" This shall be his immediate answer because he doesn't understand what Islam is.
Islam is simply telling that there is only one God.
He is only God whom we should worship and pray to and there is no other God beside Him.
He is God who sent His prophets to the world to tell people about Him.
God sent Adam, Noah, Abraham, Moses, David, Jesus, Muhammad and many other prophets (Peace be upon them all).
All these prophets came to teach people about God and guide them to God's right way.
The main teaching these prophets were concerned with in their message is that God is one.
God is the one whom people should direct their worship to.
God is the one whom they should love more than anything else.
God is the only one whom they should rely on.
God is the only one whom they should fear.
This is the main message of all prophets because this is what shall guide people to happiness in this world and in the Hereafter.
If people left God and went to anything else, they will lose happiness in this world and after they die.
This is the reason why all prophets came and this what Islam teaches.
That's why all prophets including Jesus are Muslims.
Jesus' main message was to tell people that there is only one God.
Jesus never said that he is god, but actually Jesus said the father is the only true god.
Jesus said that the eternal life is to know that the Father is the only true God and that Jesus was sent by God, which means that he is just a prophet sent from God.
Jesus never mentions the Trinity, Jesus says that he is a man and son of man, while the Old Testament says that God is neither a man nor the son of man.
Jesus says that the Father is greater than him, and that he can do nothing by himself except what is through the will of the Father.
Jesus says that the Father is his God.
This is actually the message of Islam and the Quran, and this is what Islam actually tells about Jesus, the Quran tells that Jesus says that Allah is my God and your God, so worship Him, the Quran says that Jesus denies that he said that he is God, and Jesus in the Bible never said that he is God, but kept on confirming that the Father is the only true God.
Even when he was called the son of God in the Bible, others were also called sons of God, and Jesus said that God is your Father.
Although Muslims don't agree on the idiom "Father and son", but at the end it doesn't point that Jesus is God as others were called sons as well.
This is the belief of Islam, and this is what Jesus confirmed even in the Bible, that's why Muslims say that "Jesus is Muslim".
Jesus believes as Muslims believe.
Yes, Islamic law is different from the law of Moses.
But this is because laws may change with time and place, as what Prophet Muhammad said that prophets are paternal brothers, they have one faith but different laws.
So Jesus is Muslim because he has the same faith of Muslims although he may have a different law.