Hello, good to speak with you again too.
The OT is full of important foreshadows that teach us about Christ and about God's plan of redemption. The light of Christ brings full substance to the foreshadows so that we can fully see what God was teaching us through them, which make them all the more important to continue to observe in remembrance of him. For example, 1 Corinthians 5:6-8, Paul spoke in regard to how Passover foreshadowed Christ by drawing the connection of him being our Passover Lamb, however, instead of concluding that we no longer need to bother keeping Passover now that Christ has come, he concluded that we should therefore continue to keep the Feast.
In Matthew 23:23, Jesus said that faith is one of the weightier matters of the Law and obedience to God's instructions is straightforwardly about depending on Him to guide us, so God's Law is of faith, and whatever is not of faith is sin, just sin is defined as the transgression of God's Law (1 John 3:4).
The Law points us to Christ because it is all about him, how to act like him, and how to have a relationship with him based on faith and love. If what Jesus taught was different from what the Father taught, then that would mean that Jesus was in disagreement with the Father about what conduct we should have, but I see no indication of this. On the contrary, in John 14:23-24, Jesus said that if we love him, then we will obey his teachings, if we don't love him, then we will not obey his teachings, and that his teachings were not his own, but that of the Father, so if we love Jesus, then we will obey what the Father has taught. Jesus was sinless, so he set a perfect example of how to walk in obedience to the Mosaic Law and he did not hypocritically preach something other than what he practiced, and as his followers we are told to follow his example (1 Peter 2:21-22) and to walk in the same way he walked (1 John 2:3-6).