"When it comes to being accepted by God, observing the law is completely ruled out. Here Paul makes an absolute distinction between salvation by works of the law and salvation by faith in Christ. Law-keeping cannot justify anyone.
Not that there is anything wrong with the law itself, which comes from the righteous character of God. As Paul said to the Romans, "the law is holy, and the commandment is holy and righteous and good" (Rom. 7:12) The problem with the law is our lawlessness! The reason we cannot be justified by the law is that we cannot keep it. Even if we could keep God's commandments outwardly, we break them inwardly. "No human deeds, however well motivated and sincerely performed, can ever achieve the kind of standing before God that results in the verdict of justification."
...we are acceptable to God - not by keeping the law ourselves, but by trusting in the only man who ever did keep it, Jesus Christ. The doctrine of justification can be stated in these general terms: we get right with God not by observing the law, but only by trusting in his Son...
This principle, that justification cannot come by works, is what distinguishes Christianity from other religions. Other religions try to achieve ultimate bliss by scaling God's throne through human effort, but the Bible says we cannot get to God this way. In fact, Martin Luther explained that if we try to merit grace by our works, we are simply "trying to placate God with sins." Luther meant that even our best works are tainted by evil motives. Paul had learned this universal principle from the Old Testament, for he is virtually quoting one of the psalms of David: "Enter not into judgment with your servant, for no one living is righteous before you." (Ps. 143:2). Or, as Paul translates it, "By works of the law no one will be justified" (Gal. 2:16). Total depravity extends to all humanity.
Becoming a Christian, therefore, means admitting that you cannot be saved by the good things that you do. The Galations were tempted to gain favor with God by getting circumcised. This is no longer a temptation for most Christians, but many other things are. Going to church, reading the Bible, taking communion, giving to charity - these things will never get us into heaven. Not even becoming a martyr for the cause of Christ will qualify.
There is no way to be made right with God except through faith in Christ. In Luther's words, "Now the true meaning of Christianity is this: that a man first acknowledge, through the Law, that he is a sinner, for whom it is impossible to perform any good work.... If you want to be saved, your salvation does not come by works; but God has sent His only Son into the world that we might live through Him. He was crucified and died for you and bore your sins in His own body."
- Philip Graham Ryken "Galatians: Reformed Expository Commentary - Chapter 5: The Battle for the Gospel (Galations 2:11-16) (p.63-65)