I was surprised recently to find that πρώτη πάντων (“first of all”) in Mark 12:28 is, apparently, an uncommon phrase. I spent several hours yesterday rummaging in TLG hunting for similar instances and found hardly any. Here’s my draft summary for the Baylor Handbook on this expression.
πάντων. Partitive genitive (see 8:8) referring to the entire corpus of commandments. The gender is neuter in place of the expected feminine (πασῶν, to agree with πρώτη and ἐντολή); this is probably an idiomatic, “frozen masc.-neut. form” (BDF §164.1.1; cf. Zerwick §12). A stereotyped use such as this may be used “to intensify the superlative” (Cranfield, 377). “Since πάντων, ‘of all’ (v 28), does not agree in gender with ἐντολή, ‘commandment,’ the interpretation has arisen that ‘first of all’ does not mean ‘foremost of all the commandments,’ but ‘the commandment that is more important than everything else, whether other commandments or not.’ But Jesus’ stating that there is no other commandment greater than the two he has quoted (v 31) shows that πάντων occurs ad sensum, perhaps stereotypically, to intensify the superlative ‘first’ ” (Gundry, 714). See Edwards 2002, 370, as an example of the argument which Gundry rejects. The expression πρῶτος + πᾶς in the sense “first of all” occurs less frequently in Greek literature than might be expected. The only other NT use is 1 Tim 2:1, Παρακαλῶ οὖν πρῶτον πάντων, but there πρῶτον is used adverbially. (In LXX see the related form in 2 Sam 19:21, πρότερος παντός.) TLG shows very few instances of such phrasing prior to the NT. The only such instance with a feminine form of πρῶτος (as in Mark) is Dionysius Halicarnassensis (1 C. B.C.), Antiq. Rom. 8.51.1, πρωτῃ πάντων τὰς τοῦ βίου χάριτας ὀφειλήσεις ἐμοί (“to me before all others you will owe gratitude for your life,” Loeb transl.). The only phrases with a masculine form are Hellanicus (5 C. B.C.), Frag. 85a.2 and Diodorus Siculus (1 C. B.C.), Bib. Hist. 9.3.2. With a neuter it is slightly more common prior to the time of the NT, but even then it is only found in Plutarchus (Crass. 19.6.3; Frag. 179.9), Demosthenes (In Aristog. 1, 58.4), and Diodorus Siculus (Bib. Hist. 14.5.6). There are a few other instances (but only a few) in the second and third centuries A.D.; the phrase becomes much more common in later Byzantine Greek, often in Christian writers who may have been influenced by a familiar NT phrase.
If I’ve missed something here, I’d be glad to hear of it, but I was genuinely surprised that the Greek phrase is, apparently, an uncommon one.