To avail oneself of an opportunity

If I were to be able to do something (say I'm a slave and am able to become free). What would it mean to "avail myself of the opportunity"?

What would this mean? Would this mean to take advantage of the opportunity, or to not? The word "of" is throwing me off, could someone explain the meaning here?

The question is derived from this verse in the bible:

Were you a slave when you were called? Do not let that trouble you. But if you are able to gain your freedom, avail yourself of the opportunity.
1 Corinthians 7:21

Solution 1:

“Avail oneself of X” is a fixed phrase that means approximately the same thing as “take advantage of X.” Because it’s a fixed phrase, the preposition choice is also fixed, and may not be consistent with the rules you know for prepositions in general.

The word avail is rare in modern English, and is pretty much restricted to fixed phrases, such as this one, and “[clause], to no avail” (= “they tried [clause], but it didn’t help”). The New International Version translation of this passage avoids it:

Were you a slave when you were called? Don’t let it trouble you—although if you can gain your freedom, do so.

For the hermeneutists, here’s the Vulgate and the original Greek—I can read neither, but looking up individual words gives me the impression that there isn’t anything rhetorically or theologically subtle going on in this passage.

servus vocatus es non sit tibi curae sed et si potes liber fieri magis utere

δοῦλος ἐκλήθης; μή σοι μελέτω· ἀλλ’ εἰ καὶ δύνασαι ἐλεύθερος γενέσθαι, μᾶλλον χρῆσαι.

Solution 2:

Avail [oneself] of is a common and idiomatic usage of avail:

6. avail oneself of, to use to one's advantage: They availed themselves of the opportunity to hear a free concert.

So avail yourself of the opportunity means the same thing as take [advantage of] the opportunity:

But if you are able to gain your freedom, take advantage of the opportunity.