The answer from God’s word:
To man, God’s crucifixion concluded the work of God’s incarnation, redeemed all of mankind, and allowed Him to seize the key to Hades. Everyone thinks God’s work has been fully accomplished. In actuality, to God, only a small part of His work has been accomplished. He has only redeemed mankind; He has not conquered mankind, let alone changed the ugliness of Satan in man. That is why God says, “Although My incarnate flesh went through the pain of death, that was not the whole goal of My incarnation. Jesus is My beloved Son and was nailed to the cross for Me, but He did not fully conclude My work. He only did a portion of it.” Thus God began the second round of plans to continue the work of the incarnation. God’s ultimate intention is to perfect and gain everyone rescued from Satan’s hands, which is why God prepared again to risk dangers to come into flesh.
from “Work and Entry (6)” in The Word Appears in the Flesh