The book of Galatians is a firm and thorough rebuke against anyone and everyone who seeks to bind Christians to the Old Testament Law. When Paul wrote it, the churches in Galatia were giving their ears to some unsavory charlatans, who preached, among other things, that one must still be circumcised in order to inherit the Kingdom of God, Christ or no Christ. To this day, many Christians seek to bind Christians to the law as if it was still in force today.
In reality, there are various Old Testament laws which, having been fulfilled in Christ, did not rise with him. Most Christians, for example, will admit (with a few exceptions) that the prohibition on pork is not part of the New Covenant. Christians do not have to differentiate between clean and unclean animals when they eat.
But some Christians still regard certain parts of the Old Testament as being hard and fast laws which shouldn't be broken. As a man with tattoos, this is the most obvious and common example to me, as people often cite Levitical law against them. But in Galatians 5:3, Paul tells us that those who are circumcised according to the law are obligated to keep all of it. The law is effectively an all or nothing deal. You can't appeal to it when it suits you while simultaneously opposing it when it doesn't.
A good rule when it comes to the law is this: find it in the New Testament. If a law is found entirely in the Old Testament, the chances are high it is part of the Old Covenant, designed as a guardian until Christ came (Galatians 3:24-25). The New Testament often repeats, and even doubles down on many Old Testament commands. For example, it not only repeats that murder is wrong, but that hating your brother is as bad (1 John 3:15). But other laws, such as the aforementioned law against tattoos, are mentioned once in the entire Bible, being completely absent from the New Testament. Many Old Testament laws, such as the prohibition on certain foods, and of course, as you see here, the law of circumcision, are even explicitly removed.
Ultimately, the Old and New Testaments are never supposed to be untied from each other. If you read the New Testament without looking at the Old, you will be extremely confused, because the New Testament constantly affirms, and even cites, the Old Testament. However, if you read the Old Testament without looking at the New, you will also be confused, because not only do we not have to obey all of the laws anymore, but some of them literally cannot be obeyed anymore.
As usual, context is king, and the context of the law is that it was intended to be kept by the Jews until Christ came, and then no longer. The question for those who still argue that we should keep it is are you prepared to keep all of it? The answer will always be no. You can't, and not just because the Temple has been destroyed. You can't because you're human. You're a sinner. You violate God's laws every day.
Thus, the law was designed to be kept for a short time, but the lessons we learn from it are for all time. Through the law, we learn who God is, we learn the many ways we rebel against Him, and we learn the way in which He must deal with that. But most importantly, we learn the way in which He has dealt with that. It all points to the death and resurrection of the Lord Jesus Christ, and the salvation we can only receive through faith in Him.