Main point summary
Meekly show wisdom instead of boasting in "wisdom" which is really all about you. For that is demonic, but the wisdom from God is pure, fruit-filled, and leads to righteousness.
Τίς σοφὸς καὶ ἐπιστήμων ἐν ὑμῖν;
Who is wise and understanding among you?
δειξάτω ἐκ τῆς καλῆς ἀναστροφῆς τὰ ἔργα αὐτοῦ ἐν πραΰτητι σοφίας.
By his good conduct let him show his works in the meekness of wisdom.
εἰ δὲ ζῆλον πικρὸν ἔχετε καὶ ἐριθείαν ἐν τῇ καρδίᾳ ὑμῶν,
But if you have bitter jealousy and selfish ambition in your hearts,
do not boast
καὶ ψεύδεσθε κατὰ τῆς ἀληθείας.
and be false to the truth.
οὐκ ἔστιν αὕτη ἡ σοφία ἄνωθεν κατερχομένη
This is not the wisdom that comes down from above,
ἀλλʼ ἐπίγειος, ψυχική, δαιμονιώδης.
but is earthly, unspiritual, demonic.
ὅπου γὰρ ζῆλος καὶ ἐριθεία,
For where jealousy and selfish ambition exist,
ἐκεῖ ἀκαταστασία καὶ πᾶν φαῦλον πρᾶγμα.
there will be disorder and every vile practice.
ἡ δὲ ἄνωθεν σοφία πρῶτον μὲν ἁγνή ἐστιν,
But the wisdom from above is first pure,
open to reason,
μεστὴ ἐλέους καὶ καρπῶν ἀγαθῶν,
full of mercy and good fruits,
καρπὸς δὲ δικαιοσύνης ἐν εἰρήνῃ σπείρεται τοῖς ποιοῦσιν εἰρήνην.
And a harvest of righteousness is sown in peace by those who make peace.
Real wisdom meekly shows itself. False wisdom boasts of itself.
Ac/Mn here because the boasting is in impurity (contrasting 17a)--i.e. lying to the truth.
Note the A-B-B-A structure of the text.