The Galatians “knew not God” (v.8) back when they were heathen unbelievers (cf. Jer.10:25). Back then, they “did service” to idols instead of to God (cf.Ps.97:7), idols “which by nature are no gods” (v.8). By nature, they can’t see, hear, or smell like God can (Ps.115:4-6).
When they “did service” to those idols, that made them servants to those idols, and Paul has just finished telling them that they are no longer servants (v.7). So he went on to wonder why they’d want to be in bondage again (v.9).
But right after saying they knew God, Paul remembered they didn’t know God as well as they should have. They were like the Corinthians, whom Paul said didn’t have the knowledge of God (ICor.15:34) because they’d stopped believing in the resurrection (v.12). The Galatians didn’t have the knowledge of God that said they shouldn’t leave grace for the law.
So Paul adds that they were rather “known of God” because they trusted in Him (cf. Nahum 1:7). God knew them in the sense that they belonged to Him (IITim.2:19). He knew them in the way Cain “knew” his wife and she conceived. That is, God knew them in an intimate way that made Him one with them, and made them His very own.
Paul calls the law “weak” because it was weak “through the flesh” (Rom.8:3). It was strong enough to save us if we could keep it continually (Rom.2:5-7), but we can’t, so it is weak through our flesh.
Paul called the law “beggarly” for the same reason. God promised to make the Jews wealthy in the kingdom if they could keep it continually (Deut.28:1,2,11,13). But they couldn’t, so they ended up slaves in Babylon, begging the Babylonians for their next meal. We see this pictured in Acts 3, where the lame man begging at the door of the temple, too weak to enter it, was a type of Israel under the law, begging at the door of the kingdom, too weak to enter the kingdom.
And this was the law the Galatians had put themselves under, even though God had already saved them by the power of the gospel (Rom.1:16) and enriched them with glory (Rom. 9:23,24).
The “days” they were observing (Gal.4:10) were the law’s sabbath days and feast days and “fasting” days (Jer.36:6). The “months” (v.10) were the months of the new moon (Ps. 81:3,4), and the “times” (v.10) were the times of uncleanness that women observed (Lev.15:25), and men as well. The “years” they were observing were years like the tithing year that came around every 3 years (Deut.26:12). After hearing about all that, Paul was “afraid” that all he’d heard was true, and he had labored to teach them grace in vain (Gal.4:11).
In telling them: “be as I am” (Gal.4:12), Paul meant that he wanted them to be like him and not like Peter and Barnabas. Peter was eating with Gentiles until some men from James arrived and then stopped eating with them. This caused even Barnabas to go back to observing the law’s separation law, just as Peter had done (Gal.2:9-13). Paul wanted the Gala-tians to be like him and resist the peer pressure the legalizers were giving them, just as he had resisted it (Gal.2:14).
When Paul said, “for I am as you are” (Gal.3:12), that’s a figure of speech that meant, “I’m on your side!” (cf. II Chron. 18:3). He said that because he knew it sounded like he was not on their side, that instead, he was so upset they’d left grace that he was mad at them. So he added, “ye have not injured me at all” (Gal.4:12). That is, “you haven’t hurt my feelings!” Paul didn’t take it personally when the churches he established let him down (II Cor.2:5). Other spiritual leaders often did, because it made them look like they weren’t good spiritual leaders (II Cor.13:7), but not Paul!