he was overjoyed because he had become a believer

ἀγαλλιάω (new formation in H. Gk. from ἀγάλλω, found only in Bibl. and eccl. wr.) seldom act. (B-D-F §101; Mlt-H. 225f): ἀγαλλιᾶτε 1 Pt 1:8 v.l. (for ἀγαλλιᾶσθε); Rv 19:7 ἀγαλλιῶμεν (v.l. ἀγαλλιώμεθα); ἀγαλλιῶντα GJs 17:2; ἀγαλλιῶντες ApcPt Rainer. 1 aor. (as POxy 1592, 4 [IV A.D.]) ἠγαλλίασεν Lk 1:47 (ἐπὶ τ. θεῷ, cp. Hab 3:18 v.l.); usu. dep. ἀγαλλιάομαι (Syntipas p. 75, 28); fut. ἀγαλλιάσομαι (LXX); 1 aor. mid. ἠγαλλιασάμην or pass. ἠγαλλιάθην (v.l. ἠγαλλιάσθην; B-D-F §78; Mlt-H. 225) to be exceedingly joyful, exult, be glad, overjoyed (LXX; En 104:13; TestSol 19:1 P; TestAbr A 7 p. 84, 2f [Stone p. 16]; TestJob; ParJer 6:20; ApcrEzk P 1 recto 1; Test12Patr; Mel., P. 80, 586) abs. 1 Pt 1:6 (ἀγαλλιάσαντες P⁷²); 1 Cl 18:8 (Ps 50:10); IMg 1:1; Hm 5, 1, 2; 5, 2, 3; Hs 1:6; MPol 19:2; GJs 17:2; ApcPt Rainer; my tongue exults Ac 2:26 (Ps 15:9); as here w. εὐφραίνεσθαι (Ps 30:8; 31:11; Is 25:9) Hm 5, 1, 2; Hs 9, 18, 4; χαίρειν καὶ ἀ. (Tob 13:15 BA; TestJob 43:15) Mt 5:12; Rv 19:7; cp. ἵνα χαρῆτε ἀγαλλιώμενοι that you might shout for joy 1 Pt 4:13; ἀγαλλιώμενοι προσηύχοντο AcPl Ha 1, 32; ἀγαλλιώμενος ἐσκίρτησεν 3, 17; ἀ. … καὶ κλαίειν weep for joy 6, 2. W. complementary ptc. (B-D-F §415) ἠγαλλιάσατο πεπιστευκώς he was overjoyed because he had become a believer Ac 16:34. ἠγαλλιάσοντο μεγάλως μηνύ̣[οντες] AcPl Ha 8, 5 (ἠγαλλι[ᾶτο] μηνύων BMM recto 3f). W. ἵνα foll. (s. ἵνα 2aα): ἀ., ἵνα ἴδῃ he was overjoyed that he was to see J 8:56 (B-D-F §392, 1). The one who causes the joy is given in the dat. ἀ. τῷ πνεύματι τῷ ἁγίῳ Lk 10:21 v.l.; w. ἐν and dat. ibid.—W. dat. of cause ἀ. χαρᾷ ἀνεκλαλήτῳ exult w. unspeakable joy 1 Pt 1:8. οἷς ἀγαλλιῶμαι I rejoice in this IEph 9:2 (cp. Quint. Smyrn. 9, 118 παισὶν ἀγαλλόμενος=rejoicing aloud over his sons). The object of the joy is indicated by ἐπί τινι (Ps 9:15; 20:2; Sir 30:3 al.; B-D-F §196): 1Cl 33:2; Hs 8, 1, 18; 9, 24, 2. Also ἔν τινι (Ps 88:17) J 5:35; ἀ. ἐν τῷ πάθει rejoice in the Passion IPhld ins; the acc. occurs once ἀ. τὴν δικαιοσύνην rejoice in righteousness 1 Cl 18:15 (Ps 50:16).—[ἀγαλ]λ[ι]ῶσιν a prob. restoration AcPl BMM verso 20f.—Goodsp., Probs. 192–94; WNauck, Freude im Leiden, ZNW 46, ’55, 68–80.—DELG s.v. ἀγάλλομαι. TW.