Metanoia (Repentance) - A Major Theme of the Gospel of Matthew - ChoongJae Lee

Matthew describes the beginning of Jesus''s ministry with the summary words, \\μετανοεῖτε (repent/turn), for the kingdom of heaven is at hand\\ (3:2; 4:17). Why does Matthew use this command, μετανοεῖτε, at the beginning of his ministry, and how does it relate to the rest of the Gospel? What do μετανοέω and μετάνοια mean?..