Many of His acts may have been foretold in the Old Testament, but the actions of His life are a New Testament.
The foretold actions were fulfilled. Old Testament “shadows” gave way to New Testament substance. The ark of Noah, sacrifice of Isaac, the Passover, the tabernacle, etc. All of these were shadows of good things to come (Read Hebrews 10). Christ came and Thus He lived according to the scriptures.
The New Testament was necessary because God’s plan of redemption, which had been foretold from the beginning (the just shall live by faith), reached its fulfillment in Christ’s propitiary work on the cross. Everything in the Old Testament times was pointing forward to Calvary, and everything in New Testament times points back to Calvary (with the exception of course, of Christ’s Second Coming where His enemies will be made His footstool.