"The New Covenant is not a covenant of written letters but of the Spirit; the written letters bring death, but the Spirit gives life."
This is precisely what Christ's teachings do to us, His followers. Our relationship with Him in the New Covenant is one that is spirit-filled and alive! Being alive, we can be constantly in touch with the voice of God and respond according to the Spirit.
But with his saying, "I have not come to abolish the Law but to complete it." This response to the spirit may seem contradictory. However, Jesus intended that we value the Jewish inheritance without their negative developments the Pharisees had brought about.
The whole of the Old Testament has religious value for Jesus' followers and should continue to be preserved, prayed, studied and preached as Jesus did, so as to be a new covenant for all of us. It is in this context that Jesus wanted to further condemn hypocrisy and stress the authenticity required in discipleship. Constant practice of the examination of conscience helps us to distinguish between what is for God or otherwise.
Lord, help us to be true in both our words and actions so that we may be true witnesses to Your Word.