The mystery of
the Incarnation, or the mystery of God’s becoming man, is not something that
can easily be understood by finite human minds. However, just as we
can’t fully comprehend God himself but can at least understand him at a certain
elementary level, so can we also have a basic understanding of
how it is not logically impossible for God to become man in the divine person
of Jesus Christ.

As
we have already seen, Christians believe that God is
a Trinity of Father, Son, and Holy Spirit, who each fully possess the
divine nature. Upon his Incarnation, God the Son became
man within the body of his mother, Mary. He did all this while
remaining one divine person and retaining his fully divine nature, even as he
took on a fully human nature through the Incarnation. This mystery is called
the hypostatic union, and it means that Jesus was not half God and
half man (like a Greek demigod) but was 100 percent God and 100 percent man.
How is this possible? According to the Catechism:

Christ’s human
nature belongs, as his own, to the divine person of the Son of God, who
assumed it. Everything that Christ is and does in this nature
derives from “one of the Trinity.” The Son of God therefore
communicates to his humanity his own personal mode of existence in the
Trinity. In his soul as in his body, Christ thus expresses humanly the
divine ways of the Trinity (CCC 470).

Saying
that “Jesus is God” means that Jesus is a divine person. Whatever is
true of Jesus is also true of God, even if it may sound strange at first. For
example, since Jesus died on the cross, it is also true that God died on
the cross, because Jesus is God. Of course, God did not go out of
existence,but that is not what it means to die.

Death occurs
when a being’s parts are separated into their basic elements. In this case,
Jesus’ soul was separated from his body, but God still raised Jesus
from the dead (Rom. 10:9). Since Jesus is God, then it is true that
Jesus raised himself from the dead, just as he said he would in John 2:19-21.

The Catechism goes
on to say that even though Christ had a divine nature, his knowledge was true
human knowledge; as such, it was limited, and Jesus had to go through a
process of learning to acquire it (CCC 472). This is echoed in
Luke 2:52, where it says that, “Jesus increased in wisdom and in stature,
and in favor with God and man.” Christ had human knowledge and a human
will that cooperated with the Father, but he also possessed a divine will and
divine knowledge as a part of his divine nature.

The universe
continued to function while Christ was an infant because even though the Son’s
divine nature was united to his human nature, it was
not limited by it. In his divine nature, God the Son continued to operate
in perfect communion with the other two divine persons of the Holy Trinity.
So it is accurate to say that God, in the person of the Son,
became a little baby by taking on a human nature. This doesn’t mean, however,
that a little baby possessing only a human nature was put in charge of ordering
the universe. Instead, God the Son, who was fully divine throughout his
entire human life on earth, sustained and still sustains, all of
existence. –
From 20 Answers: God