Matthew 5:43–48 contains the most radical ethical teaching in the Sermon on the Mount. Jesus commands love of enemies, prayer for persecutors, and a kind of indiscriminate generosity modelled on God himself, who sends rain on the just and unjust alike. The passage culminates in a single imperative: be perfect (teleioi, τέλειοι) as your heavenly Father is perfect.
The Greek word teleios does not mean flawless in the modern English sense. It means complete, whole, having reached the telos: the end, the purpose, the goal. A thing is teleios when it has become fully what it was meant to be. For the theosis tradition, this verse is not hyperbole but an ontological claim about human possibility. Gregory of Nyssa argued that human perfection is an endless progression into the infinite God. Maximus the Confessor held that the purpose of the Incarnation was to make this command achievable.
The text is from Codex Sinaiticus, the earliest complete New Testament manuscript.
Ἠκούσατε ὅτι ἐρρέθη · ἀγαπήσεις τὸν πλησίον σου καὶ μισήσεις τὸν ἐχθρόν σου · ἐγὼ δὲ λέγω ὑμῖν · ἀγαπᾶτε τοὺς ἐχθροὺς ὑμῶν καὶ προσεύχεσθε ὑπὲρ τῶν διωκόντων ὑμᾶς · ὅπως γένησθε υἱοὶ τοῦ πατρὸς ὑμῶν τοῦ ἐν οὐρανοῖς · ὅτι τὸν ἥλιον αὐτοῦ ἀνατέλλει ἐπὶ πονηροὺς καὶ ἀγαθούς · καὶ βρέχει ἐπὶ δικαίους καὶ ἀδίκους ·
You have heard that it was said, ‘You shall love your neighbour and hate your enemy.’ But I say to you: Love your enemies and pray for those who persecute you, so that you may become sons of your Father who is in the heavens, for he makes his sun rise on the evil and the good, and sends rain on the just and the unjust.
ἐὰν γὰρ ἀγαπήσητε τοὺς ἀγαπῶντας ὑμᾶς · τίνα μισθὸν ἔχετε · οὐχὶ καὶ οἱ τελῶναι τὸ αὐτὸ ποιοῦσιν · καὶ ἐὰν ἀσπάσησθε τοὺς ἀδελφοὺς ὑμῶν μόνον · τί περισσὸν ποιεῖτε · οὐχὶ καὶ οἱ ἐθνικοὶ τὸ αὐτὸ ποιοῦσιν ·
For if you love those who love you, what reward do you have? Do not even the tax collectors do the same? And if you greet only your brothers, what more are you doing than others? Do not even the gentiles do the same?
ἔσεσθε οὖν ὑμεῖς τέλειοι · ὡς ὁ πατὴρ ὑμῶν ὁ οὐράνιος τέλειός ἐστιν ·
Be perfect (τέλειοι, teleioi), therefore, as your heavenly Father is perfect.