In Acts 2:38 and 3:19, Peter preaches repentance like the OT prophets calling Israel to return (see 3:19; cf. 5:31; 8:22). In the immediate context, the people of Israel must repent for their corporate responsibility for Jesus’s death (2:23); but in its fuller Lukan context, the summons to repentance is appropriate for all humanity (e.g., 17:30; 20:21; 26:20), though, in that moment, Peter and his companions do not yet recognise this point (11:18). The biblical prophets summoned Israel to “turn” or “return” to the Lord (e.g., Isa 55:7; Jer 3:12, 14, 22; 4:1; 25:5; 26:3; Ezek 14:6; 18:21, 23, 30; Hos 14:1; Joel 2:12–13; Mal 3:7), which could even be summarized as their message (Zech 1:3–4).1204 Individuals also needed to turn from wickedness to righteousness (Ezek 33:14–16, 19), that is, change their lifestyle, not merely indulge in guilty feelings. Luke 3:11; 18:22 both show this by radical sacrifice of possessions for the sake of others which forms part of the answer of how to be Saved which is also the context of repentance in Acts(2:44-45)
Occasionally the Septuagint uses μετανοέω to express turning to the Lord ( Jer 8:6; 38:19 lxx [31:19 ET]; Joel 2:13; Isa 46:8),though it uses ἀποστρέφω (cf. Acts 3:26) far more frequently.The noun μετάνοια appears even more rarely (five times, all but one in the Apocrypha), though it seems to have more of a consistent association with turning from sin, particularly in later sources(i.e Sir 44:16; Wis 11:23; 12:10, 19). Apparently, however, usage had shifted by the first century; ἀποστρέφω appears just nine times in the NT(only twice in Luke-Acts) whereas μετάνοια and μετανοέω together appear fifty-two times, with a fairly consistent range of usage, including in Luke-Acts. Notice how this opposes the Baptist view of repentance which is simply changing ones mind and not turning away from sin. Sorry Baptists. It is and it requires more than just a mere confession of Christ as Lord and Saviour and includes the act of turning away from sin and sacrifices.