On the other hand, those who highly regarded God's law under the early dispensation would carry over the same respect for His word into the Christian age. Those who faithfully "do" and "teach" the commands of God (even the "least" of them) will thus be regarded as "great" in the kingdom. Clearly, greatness in the kingdom of heaven is measured by devotion to all matters of God's law--both the great and seemingly lesser obligations. Let us always have an attitude and faith that is willing to do all of what God has said simply because He has said it, even when certain things may seem trivial from our human perspective.
Jesus continues speaking about the kingdom of heaven in Matthew 5:20 - "For I say to you, that unless your righteousness exceeds the righteousness of the scribes and Pharisees, you will by no means enter the kingdom of heaven." I believe this is the key verse for the Sermon on the Mount. It contains the central idea, or thesis, for the entire sermon. A large portion of the sermon (especially from this point on) is a development of what true righteousness is in the kingdom of heaven, as opposed to righteousness under the law of Moses and the Pharisees' interpretation thereof. The primary difference that will be seen in the following verses is that the law of Moses regulated civil conduct and dealt with obvious actions of an individual while the laws of the kingdom of Christ are given to the individual to regulate his inner spiritual condition and motives of conduct.
Jesus declared that a person's righteousness must exceed the righteousness of the scribes and Pharisees if he hopes to go to heaven. The righteousness of the religious leaders was outward only, but Jesus' disciples must have spiritual righteousness that grows out of love to God and to man. It must not be self-righteousness or ceremonial righteousness but true moral righteousness--righteousness that is genuine both privately and publicly.
Before we close, let us attempt to view the rest of the Sermon on the Mount panoramically (as well as some thoughts from Matthew 4), in order to see Jesus develop the theme of true righteousness. True righteousness that exceeds: (1) Does not attempt to satisfy physical needs apart from the will of God (Matt. 4:4), (2) Does not test the Lord (4:7), (3) Serves God with undivided loyalty (4:10), (4) Sees oneself as he really is (5:3), (5) Grieves over sin (5:4), (6) Is full of meekness (5:5), (7) Sees the value in righteousness (5:6), (8) Is sympathetic (5:7), (9) Begins at the very center of life, the heart (5:8), (10) Is not self-centered but peaceful (5:9), (11) Is costly (5:10,11), (12) Brings glory to God (5:16), (13) Does not get angry without a cause (5:22), (14) Strives for reconciliation (5:24) (15) Does not lust (5:28), (16) Takes sin seriously (5:29,30), (17) Does not divorce except for sexual immorality (5:32), (18) Is trustworthy and dependable (5:34,37), (19) Does not retaliate (5:39), (20) Is benevolent (5:42), (21) Is full of love for all (5:44), (22) Seeks God's approval rather than man's (6:1), (23) Enjoys private time to commune with God (6:5-7), (24) Is concerned for God's name, His kingdom, and His will being done on Earth (6:9,10), (25) Is focused on heavenly treasures and not material gain (6:19,20), (26) Does not worry about temporal things (6:25), (27) Is not judgmental (7:1), (28) Is not hypocritical (7:5), (29) Is not gullible (7:6), and (30) Treats others as one would personally want to be treated (7:12).
Friends, does your righteousness exceed that of the Pharisees? It must if you have hopes of eternal life!