Adam Clarke on Matthew 5:20

Except your righteousness shall exceed - περισσευση, Unless your righteousness abound more - unless it take in, not only the letter, but the spirit and design of the moral and ritual precept; the one directing you how to walk so as to please God; the other pointing out Christ, the great Atonement, through and by which a sinner is enabled to do so - more than that of the scribes and Pharisees, who only attend to the letter of the law, and had indeed made even that of no effect by their traditions - ye shall not enter into the kingdom of heaven. This fully explains the meaning of the preceding verse. The old English word is right-wiseness, i.e. complete, thorough, excellent Wisdom. For a full explanation of this verse, see Luk 18:10, etc.