Legalism is usually defined as emphasizing the letter of law at the expense of the spirit of the law; that is, making sure that one complies with every iota and tiddle contained therein and yet still missing the point of what the law was intended to do.
For The Sermon on The Mount though, it is usually argued that Jesus spins this on its head and argues for the spirit of the law because in doing so, he doesn't abolish the Law or the teaching of the Prophets but rather, came to fulfill them.
Yet if I read through some parts of the sermon, we find something a little odd.
“You have heard that it was said, ‘Eye for eye, and tooth for tooth.’ But I tell you, do not resist an evil person. If anyone slaps you on the right cheek, turn to them the other cheek also. And if anyone wants to sue you and take your shirt, hand over your coat as well. If anyone forces you to go one mile, go with them two miles. Give to the one who asks you, and do not turn away from the one who wants to borrow from you.
“You have heard that it was said, ‘Love your neighbor and hate your enemy.’ But I tell you, love your enemies and pray for those who persecute you, that you may be children of your Father in heaven. He causes his sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous. If you love those who love you, what reward will you get? Are not even the tax collectors doing that? And if you greet only your own people, what are you doing more than others? Do not even pagans do that? Be perfect, therefore, as your heavenly Father is perfect.
- Matthew 5: 38-48
Ah yes. The principle of exact retribution. An eye for an eye and a tooth for a tooth. Specifically this suggests that the damage which should be inflicted upon someone as punishment, should be limited to extent of the injury of the other party and no more.
If you carefully read though one particular citation of this principle in Mosaic Law, in Deuteronomy 19 this principle is headed with a specific caveat:
the two people involved in the dispute must stand in the presence of the Lord before the priests and the judges who are in office at the time. The judges must make a thorough investigation...
- Deuteronomy 19:17-18 (part)
The actual authority in administering this exact retribution always appears to lie with the judges. In other words, just because someone has injured you, you do not automatically claim the right to claim recompense. Equity is always metered by someone in authority.
In the second paragraph of the section I've copied from Matthew, Jesus cites that it was said that one should 'Love your neighbor and hate your enemy'. Again, if you read through Mosaic law, we find that:
Do not seek revenge or bear a grudge against anyone among your people, but love your neighbor as yourself. I am the Lord.
- Leviticus 19:18.
The directive in this case is to not seek revenge or bear a grudge. Again, this would imply that the authority which exists to make good on an injury, lies elsewhere; the proper place to have a grudge properly resolved is with judges. It could also be implied that the ultimate authority to make good on an injury, rests with God himself. That would also be consistent with the law.
The reason why I point all this out is actually a pretty interesting sort of way to view the gospel itself. It kind of acts as a framing point through which to view both who the injured parties are and the one who has the authority to make good on that injury.
Jesus is the one who delivers the sermon but later on would seek to rectify the problem of sin as an injured party by not exacting retribution, which he otherwise would have been perfectly entitled to but quite the opposite.
In this case, the judge himself who logically through making a thorough investigation and pass judgement, not only turned the other cheek, walked two miles and who would in time pray for those who persecuted him, even whilst nailed to a Roman cross. If the penalty of sin is death, then exact retribution requires that that penalty be paid by the party who has caused the injury - us; yet that doesn't happen.
Jesus as part of the Godhead, has the right to claim recompense from us; yet does not. As the judge, he also has the right to administering exact retribution; yet doesn't demand payment from us but pays it himself.
Love your enemies and pray for those who persecute you? Die for them even? This is a case of a perfect judge, administering perfect justice and then exacting perfect recompense, from himself. That there is kind of mind blowing.
With all of that as a qualification, I'll now cite why I love legalism. Legalism is best fulfilled when you realise that the law is best handled by a judge.
Justice is not mine to administer. Revenge or a grudge is not something that I should or even need to pursue. It's easier to study the law, even taking note of where I fail at keeping it and have faith that the one who administers it, who has the authority to seek recompense, has the mercy and competence to do the job with mercy.
Knowing that the authority is used justly and properly, actually enables one free to live more within the spirit of the law and I know that that might sound daft but isn't that how the law is best fulfilled anyway?
It's comforting to know that a competent judge is in charge.
Legalism is formally the approach taken to analyse legal questions via logical and or deductive reasoning.
The word legalism is never used once in the bible at all. The Greek word nomos or nomon or even nomou, although does mean "law" or "custom", is never used in the context of "works"; that word is ergon.