Romans 3:1-20 - There are no good people!
So if it's not about religious practices, does that mean following them has no value? Paul says 'no' but he's specifically referring to the Jews (the Israelites of the Old Testament) who had the privilege of being shown so much by God (the 10 commandments, the rest of the law, the sacrificial system, the prophets telling of a saviour who would come). If anyone had a chance to realise they couldn't save themselves and that God was their only hope, surely it was them! They had way more information to go on than everyone else. This is why Paul says there is value in being Jewish.
Paul's main point is that there are no good people. It's all relative. If you compare yourself to a serial killer, you could say you're good but anyone who compares themselves with God has to realise they come up short - a long way short. Compared to God's goodness there are no good people. We might do some good things but this in no way helps us measure up to God. He's the only one who is truly and totally good. We are not. And Paul lumps the Jews in with the rest of humanity because he knows they need a saviour just as much as the rest of us.
Some people in Paul's day were arguing foolishly that if their sin shows how good God is by contrast, that God is unjust for holding it against them. 'But God, we were only trying to make you look good!', is not a valid excuse and is a blatant lie anyway. When we're selfish, it's because we're thinking of ourselves, not God.
Paul uses strong words to describe just how far humans have fallen from God's goodness. He's not saying no human being ever does anything good at all - it's just that when they do, it's like a drop in the ocean because the prevailing choices we make show that we generally put ourselves first instead of God.
The Jews had God's law but Paul says this isn't what makes them right. In fact, this just shows even more clearly how wrong they are and how much they needed rescuing. They should know this better than anyone else if they're paying attention. The law highlights how good God really is and how bad people really are.
Paul has been going to great lengths to describe just how bad the bad news really is. God is good but people are bad... really bad! If we can begin to appreciate the reality of our position before a perfect God, we'll be much more likely to understand the good news of Jesus that Paul is about to explain. Paul's letter so far (if we've properly understood it) should be like a dark storm cloud hanging over us but he's about to tell us his main message, which is good news!