One helpful thing that I came across was via Catholic Radio. Every so often, host Al Kresta (of Kresta in the Afternoon) has a Scripture professor as a guest, and they discuss a book of the Bible. Somewhat recently, he had Peter Williamson (Sacred Heart Seminary scripture professor) on with the topic: "where do I start with Galatians?"
A number of things struck me with Ch. 4-6...
First, Paul's "thorn in the flesh," which he mentions specifically in 2 Cor 12:7 and alludes to it in Gal 4:14. When I was in college, a priest was of the opinion that St. Paul struggled with masturbation, or at least that it was a plausible explanation. I read somewhere else that the thorn was homosexual acts. Sure, St. Paul was just as capable of sin as the rest of us, but neither of those things fit with other aspects of Paul's character.
William Barclay offered far more reasonable hypotheses than mortal sin, noting that it could likely have been epilepsy or migraines. Paul says in 4:14 that "you did not scorn me"... and in the original Greek, it literally says "you did not spit at me." It was a practice in the ancient world to spit when meeting an epileptic. (yikes) Also providing a clue is the location of the Christian community. Galatia was farther inland and less populous than Pamphylia; Paul may have originally had the latter as the target, and was forced to go to the former. Malaria was common in ancient Pamphylia, and one of the symptoms is migraines. Either way, some sort of medical condition fits so, so much better than masturbation.
Justification is a big theological topic--it has divided Christians for 500 years. I looked up the term in the Catechism and I was stunned at how short it was (#1987-2016). In the 16th Century, Martin Luther, St. Thomas More, and scholar after scholar must've wrote volumes on the subject.
A verse to memorize: "For in Christ Jesus neither circumcision nor uncircumcision is of any avail, but faith working through love." (Gal 5:6) This verse was cited by the Council of Trent in the document about justification. I haven't looked up the Protestant arguments against this yet, but I'd be interested to see them.
Barclay had a beautiful insight on the use of the word "Abba" (Gal 4:6): "It must have been often on Jesus' lips, and its sound was so sacred that men kept it in the original tongue." (pg. 35)
I often find that oft-repeated verses lose their weight in my mind. Or, if a meaning is so obvious, then leave it alone and don't complicate it further. In the case of the following passage...
Do not be deceived; God is not mocked, for whatever a man sows, that he will also reap. For he who sows to his own flesh will from the flesh reap corruption; but he who sows to the Spirit will from the Spirit reap eternal life. And let us not grow weary in well-doing, for in due season we shall reap, if we do not lose heart. (Gal 6:7-9)Pretty plain, right? The Ignatius Study Bible had an analogy that I adapted. If you plant kale, don't expect an orange tree to sprout. As an exercise, replace the two plants with something that's repugnant (kale needs a lot of help from other foods to be edible) and something that you like (an orange tree will have to do, as there is no mint chocolate candy bar tree). It helped the passage sink in a lot better for me. If I take an honest look, just how much kale have I sown? We cannot be so foolish as to take the mercy of God for granted! The things we do have eternal consequences.
St. Josemaria Escriva had a striking thought about an empty cross: the body it's waiting for is yours.
One thing I hadn't considered--was St. Paul a stigmatist? In 6:17 he says, "I bear on my body the marks of Jesus." Was he speaking allegorically or literally, or both? Or was Paul referencing his sharing in Our Lord's Passion from all the beatings he got? Here's a forum answer from EWTN a while ago.
Thank the Lord for His Word given to us!