1 John 2:5-6
5 ὃς δ’ ἂν τηρῇ αὐτοῦ τὸν λόγον, ἀληθῶς ἐν τούτῳ ἡ ἀγάπη τοῦ θεοῦ τετελείωται. ἐν τούτῳ γινώσκομεν ὅτι ἐν αὐτῷ ἐσμεν· 6 ὁ λέγων ἐν αὐτῷ μένειν ὀφείλει καθὼς ἐκεῖνος περιεπάτησεν καὶ αὐτὸς περιπατεῖν.
(5) But whoever should keep his word, by this truly their love for God is perfected. By this we know that we are in him: (6) whoever claims that he remains in him ought to walk just as even he himself walked.
Lexical and Syntactic Notes:
2:5 ἐν τούτῳ is translated “by him” to capture the idea that the love is being perfected in the entire intro condition capsulated in the “him” who follows that condition.
2:5 ἀγάπη τοῦ θεοῦ is used in the objective sense as opposed to saying “the love of God perfects…” or “this is perfected by the love of God…” (see Wallace, 121). Apolonious canon when contruction w/ initial noun and genitive noun will be either both arthrous or anarthrous. (Plummer vid lec 8.3). translated properly love for God, objective Genative.
2:5 τετελείωται is translated as “is perfected” because it is a proleptic (futuristic) perfect matching the continuous condition in the introduction phrase (see Wallace, 581).
2:6 ὁ λέγων + infinitive = “whoever claims that” indicating indirect discourse (http://www.upper-register.com/papers/GNT_syntax_notes_17_epistlesjohn.pdf Lee Irons Greek Syntactical Notes).