No one is advocating living a sinful life.
That is not supported in the NT.
However, what is also not supported in the NT is the Roman Catholic position on "mortal" v "venial" sins.....as demonstrated by the msgr's false teaching which is in contradiction of the very Ten Commandments Roman Catholics say you have to keep.
Let's go back to where Pope gets confused, and that is the difference between the Kingdom of Heaven and the Kingdom of God. Apparently he does not differentiate them, but the fact is that no person to whom God will hold accountable for even one sin can be included in the Kingdom of God.
But on the other hand, the Kingdom of Heaven (which is earth-bound) may have all kinds of sinning people in it, including those who cannot help but be deliberately sinning, as were both Peter and Judas Iscariot in their day.
While these professors though engaged in a deliberately sinful life-style may be, by earthly assembly officers, numbered with the saints, there may come a point at which such a flagrant level of sinning will cause the perpetrator to be disfellowshipped from the regular church assemby (1 Cor. 5:1-8).
I guess that kind of offense might be called "mortal" since it may mean "excommunication" (hence no salvation outside the RC); whereas tolerable sinning would be called venality, to be dealt with by "confession," absolution by a priest, and some form of "penance. The idea is to officially restore the perpetrator that he/she nay legitimately participate in communion at the "mass."
This problem of impure visible churches was one that caused Augustine to forge the myth of an invisible church that was nevertheless supervised by officers (priest, Bishops, archbishops, cardinals, etc.) over an entity that they could not see, but extending over all the individual churches.
This is why Pope, not Jesus, is inconsistent in his arguments to those inquirers who would like the truth, but are not going to get it from him.