"Therefore, leaving the principles of the doctrine of Christ, let us go on to perfection. . ."
In the verse above, "leaving" does not mean denying or ignoring; it means building upon. All the truth God reveals now builds upon truth that was revealed before.
No one truly understands or believes in John the Baptist’s baptism until he understands and believes that John’s baptism is no longer to be practiced. The truth of "one baptism" does not deny or ignore John’s baptism; it simply leaves it behind as we are brought nearer to God. If there is anyone on earth still making the animal sacrifices that Moses commanded, that person does not understand animal sacrifice as well as I do because I have left it behind. By the grace of God, I have believed those sacrifices were of God, but I am now closer to God than the Old Testament characters who had to perform such sacrifices. In Christ, I am beyond those works of the Law. In Christ, I understand those animal sacrifices, and, understanding them, I do not participate in them.
Jesus didn’t deny that Solomon had wisdom from God, but he did say that "a greater than Solomon is here." He did not deny or ignore the fact that Moses’ tabernacle or, later, the Temple in Jerusalem was holy, but he did say, "in this place, is one greater than the temple." He knew the story of Jonah was true and that the whole population of Nineveh, over one hundred twenty thousand people, including their king, repented at Jonah’s preaching. But he told a group of Pharisees, "a greater than Jonah is here." We do not deny the truth God revealed to the prophets and elders of Israel by leaving their revelation behind to draw closer to God. On the contrary, we deny that Jesus is greater than those Old Covenant men and objects when we do not leave them behind.
Paul knew that the Law of Moses was holy (Rom 7:12). He did not deny that. He made it perfectly clear to all his listeners that he understood the glory of God was in the Law and its ceremonies. Nevertheless, he had left those things behind as he built upon them to view the surpassing excellency of Christ. He wrote, "Now if the ministry of death written in letters engraved on stones was so glorious that the sons of Israel were not able to look steadily upon Moses’ face because of the glory of his countenance (which glory is being brought to an end), how is the ministry of the Spirit not more glorious? If there was glory in the ministry of condemnation, much more does the ministry of righteousness abound with glory. For indeed, that which was made glorious has come to have no glory in comparison to the surpassing glory of Christ." (2Cor.3:7-10). Paul neither denied nor ignored the holiness of the things God had given to Israel, but he left them behind. He rose above them to live in the Spirit of Christ.
In Christ, we leave behind what once were holy things, such as holy days and Sabbaths, physical circumcision, an earthly temple, the burning of incense, and ceremonial robes. We do not deny those things were of God. We leave Moses behind because a greater than Moses has come. We leave behind the burning of incense that God commanded Israel because, in Christ, we have a better kind of fire, so much purer and more acceptable to God that the old kind loses all its glory. We leave behind the animal sacrifices God commanded because a greater sacrifice has now been made, one that was so precious in God’s sight that He is now willing to forgive all the sins that have ever been committed by mankind on earth, if those people will simply approach Him in the name of Jesus for it.
Paul spoke of certain men who "profess to know God, but in works they deny Him" (Tit. 1:16). This is a wise observation. There are many who profess to know that Jesus is Lord of all, but they continue performing ceremonies as if he is not. Their works deny what their mouths profess. Don’t let your works make your words worthless. If the Messiah has really come, then let us act like it and leave behind all those things God once used to foreshadow his coming.
This is a far better covenant than the first one, so much better, in fact, that every holy and good thing in the first covenant has lost its glory. We do not deny or ignore the fact that God anointed certain people and things under the Old Covenant; still, we have left it behind because Jesus, a greater than all those people and things is here, and we refuse to deny him.