Justin Martyr on the Golden Rule

Chapter XCIII.—The same kind of righteousness is bestowed on all. Christ comprehends it in two precepts.

“For [God] sets before every race of mankind that which is always and universally just, as well as all righteousness; and every race knows that adultery, and fornication, and homicide, and such like, are sinful; and though they all commit such practices, yet they do not escape from the knowledge that they act unrighteously whenever they so do, with the exception of those who are possessed with an unclean spirit, and who have been debased by education, by wicked customs, and by sinful institutions, and who have lost, or rather quenched and put under, their natural ideas. For we may see that such persons are unwilling to submit to the same things which they inflict upon others, and reproach each other with hostile consciences for the acts which they perpetrate. And hence I think that our Lord and Saviour Jesus Christ spoke well when He summed up all righteousness and piety in two commandments. They are these: ‘Thou shalt love the Lord thy God with all thy heart, and with all thy strength, and thy neighbour as thyself.’ For the man who loves God with all the heart, and with all the strength, being filled with a God-fearing mind, will reverence no other god; and since God wishes it, he would reverence that angel who is beloved by the same Lord and God. And the man who loves his neighbour as himself will wish for him the same good things that he wishes for himself, and no man will wish evil things for himself. Accordingly, he who loves his neighbour would pray and labour that his neighbour may be possessed of the same benefits as himself. Now nothing else is neighbour to man than that similarly-affectioned and reasonable being—man. Therefore, since all righteousness is divided into two branches, namely, in so far as it regards God and men, whoever, says the Scripture, loves the Lord God with all the heart, and all the strength, and his neighbour as himself, would be truly a righteous man. But you were never shown to be possessed of friendship or love either towards God, or towards the prophets, or towards yourselves, but, as is evident, you are ever found to be idolaters and murderers of righteous men, so that you laid hands even on Christ Himself; and to this very day you abide in your wickedness, execrating those who prove that this man who was crucified by you is the Christ. Nay, more than this, you suppose that He was crucified as hostile to and cursed by God, which supposition is the product of your most irrational mind. For though you have the means of understanding that this man is Christ from the signs given by Moses, yet you will not; but, in addition, fancying that we can have no arguments, you put whatever question comes into your minds, while you yourselves are at a loss for arguments whenever you meet with some firmly established Christian. (Dialogue with Trypho §93)

Τὰ γὰρ ἀεὶ καὶ δι' ὅλου δίκαια καὶ πᾶσαν δικαιο
σύνην παρέχει ἐν παντὶ γένει ἀνθρώπων, καὶ ἔστι πᾶν γένος
γνωρίζον ὅτι μοιχεία κακὸν καὶ πορνεία καὶ ἀνδροφονία καὶ
ὅσα ἄλλα τοιαῦτα. κἂν πάντες πράττωσιν αὐτά, ἀλλ' οὖν γε
τοῦ ἐπίστασθαι ἀδικοῦντες, ὅταν πράττωσι ταῦτα, οὐκ ἀπηλ
λαγμένοι εἰσί, πλὴν ὅσοι ὑπὸ ἀκαθάρτου πνεύματος ἐμπεφορη
μένοι καὶ ἀνατροφῆς καὶ ἐθῶν φαύλων καὶ νόμων πονηρῶν
διαφθαρέντες τὰς φυσικὰς ἐννοίας ἀπώλεσαν, μᾶλλον δὲ ἔσβεσαν
ἢ ἐπεσχημένας ἔχουσιν.
ἰδεῖν γὰρ ἔστι καὶ τοὺς τοιούτους
μὴ τὰ αὐτὰ παθεῖν βουλομένους ἅπερ αὐτοὶ τοὺς ἄλλους διατι
θέασι, καὶ ἐν συνειδήσεσιν ἐχθραῖς ταῦτα ὀνειδίζοντας ἀλλήλοις
ἅπερ ἐργάζονται. ὅθεν μοι δοκεῖ καλῶς εἰρῆσθαι ὑπὸ τοῦ
ἡμετέρου κυρίου καὶ σωτῆρος Ἰησοῦ Χριστοῦ, ἐν δυσὶν ἐντολαῖς
πᾶσαν δικαιοσύνην καὶ εὐσέβειαν πληροῦσθαι· εἰσὶ δὲ αὗται·
Ἀγαπήσεις κύριον τὸν θεόν σου ἐξ ὅλης τῆς καρδίας σου καὶ
ἐξ ὅλης τῆς ἰσχύος σου, καὶ τὸν πλησίον σου ὡς σεαυτόν. ὁ
γὰρ ἐξ ὅλης τῆς καρδίας καὶ ἐξ ὅλης τῆς ἰσχύος ἀγαπῶν τὸν
θεόν, πλήρης θεοσεβοῦς γνώμης ὑπάρχων, οὐδένα ἄλλον τιμήσει
θεόν· καὶ ἄγγελον ἐκεῖνον ἂν τιμήσῃ θεοῦ βουλομένου, τὸν
ἀγαπώμενον ὑπ' αὐτοῦ τοῦ κυρίου καὶ θεοῦ. καὶ ὁ
τὸν πλησίον ὡς ἑαυτὸν ἀγαπῶν, ἅπερ ἑαυτῷ βούλεται ἀγαθά,
κἀκείνῳ βουλήσεται· οὐδεὶς δὲ ἑαυτῷ κακὰ βουλήσεται.
ταῦτ'
οὖν τῷ πλησίον καὶ εὔξαιτ' ἂν καὶ ἐργάσαιτο γενέσθαι, ἅπερ
καὶ ἑαυτῷ, ὁ τὸν πλησίον ἀγαπῶν· πλησίον δὲ ἀνθρώπου οὐδὲν
ἄλλο ἐστὶν ἢ τὸ ὁμοιοπαθὲς καὶ λογικὸν ζῶον, ὁ ἄνθρωπος.
διχῆ οὖν τῆς πάσης δικαιοσύνης τετμημένης, πρός τε θεὸν καὶ
ἀνθρώπους, ὅστις, φησὶν ὁ λόγος, ἀγαπᾷ κύριον τὸν θεὸν ἐξ
ὅλης τῆς καρδίας καὶ ἐξ ὅλης τῆς ἰσχύος, καὶ τὸν πλησίον ὡς
ἑαυτόν, δίκαιος ἀληθῶς ἂν εἴη.
ὑμεῖς δὲ οὔτε πρὸς θεὸν
οὔτε πρὸς τοὺς προφήτας οὔτε πρὸς ἑαυτοὺς φιλίαν ἢ ἀγάπην
ἔχοντες οὐδέποτε ἐδείχθητε, ἀλλ', ὡς δείκνυται, καὶ εἰδωλολάτραι
πάντοτε καὶ φονεῖς τῶν δικαίων εὑρίσκεσθε, ὡς καὶ μέχρις
αὐτοῦ τοῦ Χριστοῦ τὰς χεῖρας ἐπιβαλεῖν ὑμᾶς καὶ μέχρι νῦν
ἐπιμένειν τῇ κακίᾳ ὑμῶν, καταρωμένους καὶ τῶν τοῦτον τὸν
ἐσταυρωμένον ὑφ' ὑμῶν ἀποδεικνύντων εἶναι τὸν Χριστόν· καὶ
πρὸς τούτοις ἐκεῖνον μὲν ὡς ἐχθρὸν θεοῦ καὶ κατηραμένον
ἀξιοῦτε ἀποδεικνύναι ἐσταυρῶσθαι, ὅπερ τῆς ἀλογίστου ὑμῶν
γνώμης ἔργον ἐστίν.
ἔχοντες γὰρ ἀφορμὰς ἀπὸ τῶν γενο
μένων σημείων διὰ Μωυσέως συνιέναι ὅτι οὗτός ἐστιν, οὐ βού
λεσθε, ἀλλὰ καὶ πρὸς τούτοις, ἡμᾶς ἀλογεῖν δύνασθαι
ὑπολαμβάνοντες, συζητεῖτε ὅπερ ὑμῖν συμβαίνει, καὶ ὑμεῖς ἀπο
ρεῖτε λόγων, ὅταν εὐτόνῳ τινὶ Χριστιανῷ συμβάλητε. (PG Migne VI,??)