Matthew 5:27-28 "You have heard that it was said, 'You shall not commit adultery.' But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.
Matthew 5:31-32 "It was also said, 'Whoever divorces his wife, let him give her a certificate of divorce.' But I say to you that everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery. And whoever marries a divorced woman commits adultery.
KEY THOT: Regarding the OT Law and Prophets, Jesus says he did not come "to abolish them but to fulfill them" (Matthew 5:17). And then he illustrates what he means from the OT laws on murder, adultery, divorce, oath, compensation, and love for neighbours (Mt 5:21-48). In every instant, Jesus begins by saying: "You have heard it was said..." (in other words, how it was taught by the scribes). But he then goes on to explain how to truly fulfill the intent of the law: "But I say to you..." (this is how it should be done). The scribes taught that obedience to the law consisted in outward actions. But Jesus says that obedience to the law consists in inward attitudes and intentions. So anger is murder (v.21), lust is adultery (v.28), divorce facilitates adultery (v.32), honesty is integrity (v.37), justice is giving away, not getting our rights (v.39), and love for our neighbors must include our enemies.
So, Jesus did not throw away the OT laws--he fulfilled its inward reality in his own life and expected his disciples to do likewise through His Spirit. Jesus fulfilled the law at its root: in the thought life of our heart. All transgressions of the law takes place in our thoughts and our obedience and fulfillment of the Law and the Prophets must occurred in our heart--i.e. our attitudes and motivations. Only when we allow the Spirit of God to apply His Word as His Sword in our heart that we can discern and distinguish between thoughts and intentions of our heart: "For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit... and discerning the thoughts and intentions of the heart" (Hebrews 4:12). The Word of God will renew our thought-life to fulfill the Law's intents.
That is why Jesus told his disciples that their righteousness must exceed that of the scribes: "For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven" (Matthew 5:20). The righteousness of the scribes comprises of regulations, rules and rituals. We can do all of these things while still harboring ungodly thoughts and motives. We can even do good works like ministry, community service, etc. but not to seek God's pleasure, but men's approval and applause. So, the scribal righteousness is based on outward performance. But the kingdom righteousness is based on inward intentions to please God, not men.
Father, help us obey Your Law by aligning our attitudes and thoughts with it, so that we may truly fulfill it from our heart. Amen.