I hear a lot of non-believers say things like the OT and NT are not congruent, and in the Old there was a set of "silly" rules, that no one could follow, and no one should follow, and then in the NT we see a complete reversal where the rules are softer, or something.

First I couldn't disagree with that idea more, because Jesus was very firm that the old rules weren't taken far enough. Matthew 5:29, if your eye causes you to sin, tear it out...

So its clear from Jesus teachings that behaviour matters HOWEVER, Not as a means to securing our own salvation. Salvation only comes through faith in Him who could earn that salvation for you/me, whjo .

Matthew 5:17
Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them, but to fulfill them.

I used to wonder what he meant by fulfill, and I still do not fully get it, but it seems to me that its like this:

1. God made the law in order to best direct us, and lead us to the best life possible, attempting to produce a God honouring nature in our hearts and minds.
2. We failed to abide the law, and when we do we do so for the wrong reasons (ie., to be seen abiding, such as the pharisees who pray with big words, in public places.)
3. So Jesus came, lived a sin-less life, despite facing all the temptation we face.

• Hebrews 4:15, "For we do not have a high priest who is unable to sympathize with our weaknesses, but one who in every respect has been tempted as we are, yet without sin."

1. And so in Jesus' totally undeserving death, he was charged the ultimate unfairness, dishonour, pain, and persecution, and it paid for our sin debts. Its like true righteousness is currency, and we have none to pay the debt of sins incurred, but He who lived blame-less could pay all our ransoms.

I dont know if that helps anyone, and maybe its just for me, but I certainly find discussing, writing and thinking scripture is the best way for me to wrap my head around it, so thanks for this opportunity.

Blessings.