1 John 2:8

πάλιν, “again,” i.e. in another sense, from another point of view, not in itself but in our recognition of it, “it is a new commandment”. ὅ ἐστιν ἀληθές, in apposition to ἐντολήν “a thing which is true,” viz., the paramount necessity of Love. This truth, though unperceived, is contained in the revelation of Jesus Christ (ἐν αὐτῷ) and proved in the experience of believers (ἐν ὑμῖν). It is a fact that hatred of one's brother clouds the soul and shuts out the light. “I know this,” says the Apostle, “because the darkness is passing away and the light, the true light, is already shining,” i.e. my eyes are getting accustomed to the light of the Gospel-revelation, and I have seen this truth which at first was hidden from me. Adjectives in - ινός denote the material of which the thing is made; and ἀληθινός is used of the real as opposed either to the type (cf. John 6:32; John 15:1; Hebrews 8:2; Hebrews 9:24) or to the counterfeit (cf. Symb. Nic. : Θεὸν ἀληθινὸν ἐκ Θεοῦ ἀληθινοῦ “very God of very God,” i.e. the real God as opposed to false gods, idols, which were “things of naught”). The opposite of to τὸ φῶς τὸ ἀληθινόν is, on the one hand, the dim light of the Jewish Law (the type) and, on the other, the false light of human speculation (the counterfeit).