"Christians" -- followers of Christ -- do not consider his teachings something to be ignored. Otherwise, we'd be called "Paulians".
He was sent “only to the lost sheep of the nation of Israel”
There isn't one Gospel for Jews and another Gospel for Gentiles -- Paul himself makes this crystal clear in Romans! -- so the Gospel Jesus preached is just as valid for Gentiles as it is for Jews, even though he left the evangelization of the Gentiles to others.
post-Resurrection believers who are NOT UNDER LAW BUT UNDER GRACE
You really have to misread Romans to not understand that EVERYONE IS UNDER GRACE, AND ALWAYS HAVE BEEN, no matter what the Pharisees and Judaizers preached.
I’m not a Paulian, nor do I disregard any of Jesus’ words or any words in Scripture. Remember, you are the one stuck in the Labyrinth and it’s cascading layers of extra-biblical cant. The CCC and Trent do NOT agree with Paul’s clear and sound teaching on grace, with their hem-hawing and self-dooming anathemas. I would say to you “Look for the exit!” But I’m a realist when it comes to this.