The “liberty” Paul says to “stand fast” in is the one that makes us “free” from the law (5:1). We need to be free from this “ministration of condemnation” (IICor.3:9) because it demands 100% obedience 100% of the time (Gal.3:10). You couldn’t give that before you were saved, so the law condemned you, and you asked God to save you by grace.
But you still can’t keep it, so the law still condemns you. Not to hell, but to feeling condemned, so “stand fast” in grace instead (Gal.5:1). “Fast” means immovable (Acts 27:41). The Galatians moved (Gal.1:6), and got “entangled” in the law (5:1), the way the Jews were trapped by the Red Sea (Ex.14:2,3). They probably felt hopeless, and you will too if you put yourself under the law, since you still can’t keep it.
Paul calls the law “the yoke of bondage” (Gal.5:1) because telling men “thou shalt” and “thou shalt not” is how you treat slaves, and slaves feel hopeless because they are trapped. You are “free from the law” (Rom.8:2), so stand in grace!
Paul interjects the subject of circumcision in this discussion of the law (Gal.5:2) because it was the first thing a Gentile had to do to be saved under the law (Ex.12:48). But the Galatians got saved under grace, so Paul said if they got circumcised “Christ shall profit you nothing.” It can’t take away the profit we already have, i.e., salvation (ICor.10:33). But the law can rob you of the additional profit Christ can give you.
Doing the first thing the law tells you to do obligates you to do all the things the law says to do (Gal.5:3), and you can’t, so you’re cursed (3:10). The law can’t curse you to a loss of salvation, but to a loss of “blessedness” (cf.4:15), i.e., thankfulness (Mark 6:41 cf. John 6:11). And thankfulness is the basis for all we do. We don’t do good works to get saved, but to show God we’re thankful He saved us. Thankfulness leads to a happy life—the additional profit Christ can give!
No man is justified by the law in the sight of God (Gal.3:11), so the ones whom Paul says “are” justified by it (5:4) are justified in their own eyes. That means they were “fallen from grace.” People use that verse to say we’re saved by grace, but you can sin too much and lose the salvation you got by grace. But the Galatians were religious, not sinful like the Corinthians. Paul didn’t tell them they fell from grace. He told that to the Galatians because falling from grace in the context means not standing in grace (5:1). Grace justifies you 100% from “all” things (Acts 13:39). If you think you’re justified by the law, and you only keep the law 90% of the time, you’re only 90% justified. To get from 100% justification to 90% justification, you have to fall.
Now, to get 100% righteousness in your conduct, you’ll have to “wait” for it (Gal.5:5). That’s our “hope” of righteousness, and “hope” means trust (Ps.71:5), confidence (Job 4:6) and expectation (Pr.10:28). We wait for this hope “through the Spirit” (Gal.5:5) the same way Paul says we wait for it in Romans 8:23 through the Spirit. There the Spirit helps us when we “groan” in pain (Rom.8:23) by reminding us through the Book He wrote that we are children of God (8:15) and will someday be 100% healthy. And when we grieve the Spirit, He helps by reminding us that someday we’ll be 100% righteous in our conduct as well as in Christ.
“Avail” (Gal.5:6) means to profit (Mark 8:36), so when Paul says circumcision can’t “avail” us, it’s another way of saying again that it can’t “profit” us (cf.Gal.5:2). There’s also no profit in “uncircumcision” (5:6), i.e., no profit in just avoiding circumcision and the law. There were “spiritual” Galatians who did avoid it (6:2), but that’s not what made them spiritual! “Faith which worketh by love” did (5:6). What’s that? Well, faith is believing God (Rom.10:17), and if you believe what God says, you’re going to do good works in any dispensation. But faith that works by law helps your brother because God says you must (Deut.15:7,8). Faith that works by love helps a brother because you love him!