OTC, Kristina, it was quite impossible for Him to sin, since He is God Incarnate and God cannot sin. This is the teaching of the Church, that the God-Man was impeccable (could not sin).
Christ as a healer must have what He is going to share, i.e., must be fully, i.e., perfectly human and Divine or He could not heal us. He gives us the health, as it were, He has. If He did not have this health we, being sick, could not receive healing.
He therefore has the fully human nature, i.e., one not wounded by sin. His humanity is therefore graced and in harmony with the Divine. For us to be tending toward sin is for us not to be fully human; therefore we are not the vantage point of healing of our wounded nature but He is. It follows that for Him to heal our infirmity He must bring health to our infirmity. We can’t give what we don’t have, so He must have this health of being fully human, i.e., in harmony with God in order to give it to us by grace. He therefore could not sin, which makes him perfectly human, not less human.