14 For by one offering he hath perfected for ever them that are sanctified.
15 And the Holy Spirit also beareth witness to us; for after he hath said, 16 This is the covenant that I will make with them After those days, saith the Lord: I will put my laws on their heart, And upon their mind also will I write them; [then saith he,] 17 And their sins and their iniquities will I remember no more.
18 Now where remission of these is, there is no more offering for sin.
So then this is a quote from the OT, and it is called out for context.
"for after he hath said . . ." "And their sins and their iniquities I will remember no more."
The point the writer is making, seems to me, then that are sanctified are perfected forever by one offering, their sins having been forgotten.
And to support this, the writer notes that after is it written that God will make a new covenant wherein He would write His laws on their hearts, after He says about this, He goes on to say that their sins will not be remembered.
So, rather than affirming a covenant of Law upon the Christian, the writer affirms the forgiveness of sins found even in the same place as this other statement.
So then we need to ask, this other statement, about laws being written on hearts, to whom does it apply?
So we need to track down the quote, and examine the context, and parallel passages, and answer all those first questions, who, what, when, how, why.
Much love!
PS . . . and then I read your post about the written law being for the lawless, and, Yes!