Jesus is a Human Being, he was descended from human beings, & inherited their chromosomes.
God is not a human being, He is above that, He is a "God"
God doesn't have to turn in to a human to make people believe in Him, He sent Prophets & Holy Books & gave us the free choice to believe or disbelieve.
Christians ask: if God isn't his father, who is his father?
The Holy Quran answers: "Indeed, the example of Jesus to Allah is like that of Adam. He created Him from dust; then He said to him, "Be," and he was." Surat Al-Imran
But why did God ordain that (i.e. to give Jesus that miraculous supernatural birth from a mother without a father)?
Jews –to whom Jesus was sent- were very MATERIALISTIC, their hearts were as hard as stones or even worse. When u read the Old Testament you'll find it concentrating on (the material): the decoration of the temple, the uniform of the priests, the names, the numbers, the statistics, etc…
So God sent them a spiritual miracle which is against material & beyond natural laws; a human from a mother without a father.
Jesus himself came up against their materialism later:
when the disciples asked him why he spoke to Jews in parables, he answered that "For this people’s heart is waxed gross" (look at Matthew 13: 10- 17).
Jesus pronounce woes upon the scribes & Pharises many times because of their materialism, e.g. when he described them as "whited sepulchers" (which indeed appear beautiful outward, but are within full of dead men’s bones, and of all uncleannss ) Matthew 23: 27
also he tried to make them understand that religion is not just ceremonies & rituals, but it is a light in the heart, a mercy, a faith, a piety.
e.g.: "11 Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth, this defileth a man." Matthew 15: 11
On the other side Christians were extremely spiritual, they made him a god & third of three & worshipped him.
But Islam is in between & gives you the whole truth, " O People of the Scripture, there has come to you Our Messenger making clear to you much of what you used to conceal of the Scripture and overlooking much. There has come to you from Allah a light and a clear Book." Surat Al-Ma'idah