Gabriel figured that people do not deserve God's mercy and
love... and that people needed to show themselves worthy of God's
love and mercy... in there, it showed himself betraying God, by
saying that it was greater than God and could speak for
God...
in Gabriel's plan, in order to have the people have enough stress
and trauma in order to prove themselves worthy, Gabriel would
unleash the son of Lucifer onto Earth... as the son of Lucifer is
more horrific than Lucifer...
then you see everything that happened...
Gabriel, in his sacrifice of his own life, in order to have Isobel
saved from the fires of Hell, finds redemption.. and Lucifer,
refusing to admit defeat that he has lost Constantine to God, rips
out the cancers from Constantine, so that Constantine will "fall"
again...
cool movie, but not groundbreaking.. look for sequels...