Paul's plea here is found in numerous other epistles as well, where he beseeches his readers to follow him: "Imitate me, just as I also imitate Christ" (I Corinthians 11:1; see also I Corinthians 4:16; Philippians 3:17). Paul is not trying to put himself above God or establish a position for himself; Philippians 3:17 gives the reason: "Brethren, join in following my example, and note those who so walk, as you have us for a pattern." Paul is pointing to himself as an example, as someone more spiritually mature and experienced—someone who knows the ropes and understands the consequences of the weighty decisions the Galatians were facing.
The Galatians appear to have been spiritually immature. Had they been of the same mind and inclination, they would not have rejected authority (a sign of immaturity), and Paul would not have had to concentrate so much on establishing his credentials at the beginning of the letter. When children do not respect their parents' advice, they grow up missing the significance of much that they encounter and slow the development of wisdom. Similarly, if the Galatians were rejecting the authority that Christ gave to Paul, it is likely that they were not of a wise or mature mindset, which explains the foolishness they were exhibiting (Galatians 1:6; 3:1, 3; 4:9).
Paul has just finished a stern and lengthy rebuke of the Galatians, which they may not have responded to well if they were spiritually immature and rebellious. His tactic changes here, as he urges them to consider his own example and conduct as a guide. Rather than just telling them what to do, he also shows them.
If the Galatians followed Paul's example, they would have kept the Sabbath (Acts 13:13-14, 42, 44; 16:13; 17:2; 18:4), observed the holy days (Acts 18:21; 20:6; I Corinthians 5:7-8; 16:8), obeyed God's law (Romans 2:13; 3:31; 6:15; 7:7, 12, 14, 16, 22, 25; 8:7; I Timothy 1:8), and at the same time abstained from the customs, rites, and traditions of Judaism (Acts 22:3; 26:4-6).
The phrase translated as "become as I am, for I am as you are" is misleading in its verb tense. A closer rendition would be "become as I am, for I became like you." Paul is exhorting the Galatians to follow his example, to take the same steps that he did in renouncing the traditions and stumbling blocks of Judaism. He encourages this "because I became like you"—that is, in the past he was so consumed by Judaism (Galatians 1:14) that he was exactly where the Galatians were now or would be shortly: rejecting the word and law of God in favor of the "traditions of the fathers," whose emphasis was on being able to save oneself through a personal level of righteousness.