"So as with the other covenants, it is possible for someone to join the new covenant community externally without the new heart that defines that covenant. He may be baptized and profess Christian doctrine. But if he lives a life of sin, he shows that he does not have the new heart that is the mark of the new covenant. He has wrongly entered the covenant community and ought to be disciplined by the body. He has become a Christian externally, but without inward change." - Frame, ST, p81
While straightforward, reformed, evangelical doctrine, this is actually a very controversial way of looking at the New Covenant in our circles. Some would argue that there is no "inward" or "heart" change in the new covenant believer because we are still the same person. Rather, we are indwelt by the Spirit and then discipled by Him as we mature. If we reject this discipleship, we prove ourselves to be apostates and not of the final elect.
This way of looking at the New Covenant has some strength to it. It discourages peering into hearts or even a temptation to do so. On the other hand, it seems to contradict many portions of Scripture which speak of a new man, a new nature, a new creation that we have become in Christ, and warn of lips that speak the praise of God while hearts are full (inwardly) of defilement and lusts.