The purpose of the Gospel is to change you by God’s grace. What this change looks like is revealed to us in the Law of God first given at Sinai but then fulfilled perfectly by Christ as he established to New Covenant and calls us by grace to live under his Lordship. So we need the Holy Spirit to work this change in our lives and we have him doing just that but we also need to understand the Law of Christ for all the reasons stated or we risk getting the gospel wrong!