"You have heard it said ... but I say to you ..." There are a number of commandments, laws and customs that Jesus talks about in this way, in this part of His 'sermon on the mount', in St Matthew's gospel (Matt 5). He's not contradicting the laws, or changing them, or much less abolishing them altogether. In fact His purpose is to 'fulfill' the law. But His "re-interpretation" doesn't mean making the law more strict or difficult to observe, although perhaps at first sight that may be the impression the gospel gives. Rather, for the new Kingdom of God Jesus is laying down a higher standard of observance and behaviour, a deeper response to God, a response in spirit rather than in mere following of the letter. Quite often when people talk about the 'spirit' of something, there's an implication that the corresponding 'letter' is too inconvenient or difficult, and can thus be by-passed. But this is the opposite of what Jesus was saying. For Him, the 'spirit' of the law was a deep heartfelt response to God, going well beyond the surface words and their demands, going to the root of love, fulfilling the law. What Jesus says about losing an eye or a hand rather than infringing the high standard of upright behaviour that He sets seems extreme to some people. But it is a matter of values, the extremeness of someone who will not let anything stand in the way of being faithful to God's love and His commandments and will for them.