When you do not study the entire bible, it is hard to understand all God says in His word. You also need an understanding of what the world was like that Paul was addressing. All the letters to the various churches were reporting God's words, and they report truths, but we can understand those truths better by knowing what brought about the need to write.
God in one scripture said to be circumcised, God wouldn't tell in another it is wrong to be circumcised.
The problem that was being addressed was that the Jews, who were the majority of the Christians at the time, thought that becoming a Christian meant gentiles must adopt the lifestyle Jews had been taught. The gentiles, to a man, had lived a lifestyle developed around pagan worship. When the Jews taught that it was about eating and holidays instead of the things we learn about from Paul, God said to tell the gentiles that wasn't at all what it was about.
Circumcision was about taking off some flesh as a reminder and sign that they would remove sin from their lives and put on obedience. In the beginning circumcision was done without knowing why. After Christ and after we received the HS we were told why, and that it wasn't the removal of skin that was important, but what it signified. We could be circumcised without the removal of skin, it wasn't the skin that was important but the heart.
It is just as wrong to say that you must not circumcise as a reminder as it is to say that the taking of skin is all that is required. What is important in our being circumcised in the heart.
