The book of Hebrews repeats a central reason that God gave a new law four specific times.  He first tells us that if it were not weak and unprofitable, we would not have had a need for a High Priest to arise after the order of Melchisedec.  What did its weakness and unprofitableness prevent the Law from doing?

If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?  (Heb. 7:11).

We note the problem.  Perfection was not possible under the Levitical priesthood.  Thus there had to be a new high priest who could give the New Testament. He gives the same reason again for stating that the Old Testament law was weak and unprofitable.

For there is verily a disannulling of the commandment going before for the weakness and unprofitableness thereof.  For the law made nothing perfect, but the bringing in of a better hope did; by the which we draw nigh unto God (Heb. 7:18-19).

We note here that the same clarification is offered again for giving the New Testament.  The law made nothing perfect.  A third time he gives the same explanation – the Old Testament priests were offering “. . .gifts and sacrifices, that could not make him that did the service perfect, as pertaining to the conscience” (Heb. 9:9).  A fourth time he offers the same truth:

For the law having a shadow of good things to come, and not the very image of the things, can never with those sacrifices which they offered year by year continually make the comers thereunto perfect (Heb. 10:1).

Who could rightly deny that making men perfect is a primary reason for giving the New Testament?

He prefaces these statements above in chapters 7 through 9 by directing God’s children to the goal of the disciple in chapter 6 when he said:

Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying again the foundation of repentance from dead works, and of faith toward God (Heb. 6:1).

His purpose is clear and obvious.  Jesus is our example and captain of our faith who attained that very goal.

For it became him, for whom are all things, and by whom are all things, in bringing many sons unto glory, to make the captain of their salvation perfect through sufferings (Heb. 2:10).

Our Father made Jesus perfect.  He was not born perfect, for he was made perfect ‘through sufferings.’  He learned obedience by the things which is suffered (Heb. 5:8).  Though he was a Son, he had to learn the same way all of God’s children learn.  As he ran the race ahead of us (was ‘made perfect’) he became the author of eternal salvation to all who will obey him (Heb. 5:9).  “For the law made nothing perfect, but the bringing in of a better hope did; by the which we draw nigh unto God” (Heb. 7:19).  Jesus and the new covenant is that better hope which does make men perfect, like Christ (Luke 6:40).  Thus the Old Law had to be done away to make way for the New Law, the perfect law of liberty.  Only a perfect law can make men perfect.