Merry Christmas! Allow me to draw a little diagram to depict, in a much unsophisticated way, salvation history.
The starting point (the triangle) would be God. “In the beginning was the Word, and the Word was with God, and the Word was God” (John 1:1). The Holy Trinity always existed. God experiences within himself nothing but love and joy. He decides to share this, so he creates the world. God, creation, and mankind are one (the globe). Unfortunately, Adam and Eve sin, so God departs, leaving he and mankind separate (the apple). But God doesn't remain separated from his beloved creation forever. He comes back down to earth by sending his Son. This moment would be the Incarnation (the Christmas tree). The period of time, by the way, between the globe and the Christmas tree would be the Old Testament. Jesus lives on this earth for 33 years, teaching us about God and about ourselves, and redeems mankind so that we and God can be united as we were originally in the beginning. Christ does not remain physically on this earth permanently, however. He ascends back to his Father in heaven (the cloud). But this is not like the absence from before when Adam and Eve sinned. God comes back down to us in the Holy Spirit at Pentecost (the flame). The period of time between the Christmas tree and flame would be the New Testament. Now we have God permanently on this earth. We experience his presence in the Church and particularly in the sacraments (the church).