That's the beauty of Paul's writings. You have to ask, "now why did he say that?". And then that leads you to a deeper truth.

Your example about the law being a curse is a good one. It would take literally an entire college level bible study class to scratch the surface on that one. But perhaps this one verse will make the light come on:

Before this faith came, we were held in custody under the Law, locked up until faith should be revealed. So the Law became our guardian to lead us to Christ, that we might be justified by faith. Now that faith has come, we are no longer under a guardian.… - Galatians 3:24

So he is saying that the Law is still in full force and those who choose to be governed by it must keep it perfectly. But Jesus said that he was providing a new covenant that would be much easier to keep than the Law - you just have to give up any claim that you can save yourself and rely on Jesus' free gift (his sacrifice on the cross to pay any and all penalties you have accumulated for being a Law breaker.)

So, do you see that Paul is not being inconsistent. He is explaining how things are in term of the old and new covenants that God is laying side by side for comparison.

The purpose of the Law was to point out why we needed a savior.

All the rest of Paul's teachings are dealing with the same kind of issues.

Read Romans 14 in one sitting and ponder the depth. "All things are legal for me but all things are not profitable" I'm a grown-up now. I no longer need my guardian to tell me not to eat too many cookies. I can watch my own weight and manage my own health from First Principles, not a guardian's rules.

Thus I can eat meat sacrificed to idols because God knows that I know that he owns every T-bone steak in the world and I'm thanking Him for it. BUT, if eating that steak would make some other Christian feel guilty, I won't do it. If he sees me eat and follows my example while believing he is disobeying God - then for him it IS sinful. His sin is deliberately doing something he thinks that God sees as wrong, not the actual eating of the steak himself.

So my grown-up motives are entirely different. I'm restricting my own freedom, when necessary, for other people's benefit.

That's why Paul had Timothy circumcised. He and Timothy both knew it was not necessary and that Timothy was not depending on such an act for his own salvation. But they did it anyway for the sake of the Jews Timothy was reaching out to. This simply removed one more argument that might otherwise get in the way of him reaching a certain category of people.

It is in that sense that Paul says, "I have become all things to all men so that by all means I might save some."

Of course, anyone he reaches will eventually mature and have these things explained to them. Paul is just removing obstacles for making initial relationships with people.

The same thing applies to the ceremony he agreed to do in the Temple. He knew he couldn't reach his own people if he was seen as disregarding their ceremonial law. He knew it wasn't necessary, but for them it was necessary, and so he complied.