John Owen on the difference bewtween the covenants

John Owen, in his work The Death of Death in the Death of Christ emphasizes the main difference between the old and new covenants:

And this is the main difference between the old covenant of works and the new one of grace, that in that (he Lord did only require the fulfilling "of the condition prescribed, but in this be promised to effect it in himself with whom the covenant is made. And without this spiritual efficacy, the truth is, the new covenant would be as weak and unprofitable, for the end of a covenant (the bringing of us and binding of us to God), as the old. For in what consisted the weakness and unprofitableness of the old covenant, for which God in his mercy abolished it? Was it not in this, because, by reason of sin, we were no way able to fulfil the condition thereof, " Do this, and live?" Otherwise the connection is still true, that " he that doeth these things shall live." And are we of ourselves any way more able to fulfil the condition of the new covenant? Is it not as easy for a man by his own strength to fulfil the whole law, as to repent and savingly believe the promise of the gospel? (237)

The main difference being the promise of the Lord who effects in his chosen ones the condition prescribed in the new covenant. For indeed, it would be just as easy for a man to fulfill the whole law as opposed to repent and savingly believe in Christ. In either case, without help, without grace, we are doomed to be unsuccessful.