Adam Clarke on Matthew 7:18

A good tree cannot bring forth evil fruit - Love to God and man is the root of the good tree; and from this principle all its fruit is found. To teach, as some have done, that a state of salvation may be consistent with the greatest crimes, (such as murder and adultery in David), or that the righteous necessarily sin in all their best works, is really to make the good tree bring forth bad fruit, and to give the lie to the Author of eternal truth.