Jude 1:20

ἐποικοδομοῦντες … πίστει. Polycarp’s letter to the Philippians (iii. 2) seems to contain a reminiscence of this (Bigg and Mayor). “If you study the epistles of the blessed Apostle Paul, δυνηθήσεσθε οἰκοδομεῖσθαι εἰς τὴν δοθεῖσαν ὑμῖν πίστιν.” St Paul often uses the metaphor of building, notably in Ephesians 2:20 sqq. The solidarity of the brotherhood is contrasted with the divisions introduced by the ἀποδιορίζοντες.

πίστει, used very much as in Jude 1:3.

ἐν πνεύματι ἁγίῳ προσευχόμενοι, cf. Ephesians 6:18 προσευχόμενοι ἐν παντὶ καιρῷ ἐν πνεύματι.