It's a good example. I'd say, do not do what he did. This applies to our pastors or anyone we look up to if they don't go by the Word.
Yet many are not claming Paul to be a mere "pastor", but an "apostle" with a much greater standard.
On the other hand, does this law apply to believers now? And what was/is the meaning of appearing before Him in Jerusalem 3 times a year?
The appearance was to Jerusalem (Psa 84:7) at the Temple to present offerings (Deu 16:16,17; 12:5,6), and to learn of YHVH's Torah/Law (Deu 31:11-13). Since the Temple is not extant, it is my belief that this particular law does not apply to faithful believers now.
Makes sense if Peter didn't say "Bear in mind that our Lord’s patience means salvation, just as our dear brother Paul also wrote you with the wisdom that God gave him." in verse 15 which confirmed
a. Paul is a brother in Christ.
b. God gave Paul wisdom to write.
In fact, there's much wisdom in his teachings that is hidden from the world c.f. 1 Cor 2:6-16.
1. The Greek text of 2Pet 3:15 does not include "
God gave him". It only says "wisdom given him". The Greek text does not identify the source of Paul's wisdom. James 3:15 states that there is a devilish sort of wisdom.
2. The Greek text does not identify Paul as a "brother
in Christ". Only as a "brother". Not all "brothers" are good brothers, cf Mt 10:21.
3. Whatever hidden wisdom Paul allegedly reveals, is it witnessed to by additional writers? Or preached only by Paul alone? Is Paul greater than Messiah's standard for Himself (cf Jn 5:31)?
Now to his teachings, the obvious one that doesn't go well with the law is circumcision, if we don't believe that the OT has already taught circumcision in the heart. So what do you say?
The Tanach teaches that circumcision of the heart
and flesh are both necessary. Faith plus obedience, which Messiah, and the twelve, and James the elder all preach.