Matthew 4: 17 in Greek reads
Μετανοεῖτε˙ ἤγγικεν γὰρ ἡ βασιλεία τῶν οὐρανῶν.
A word for word translation
Repent / change your mind approaches for the realm of the heavens
Μετανοεῖτε Μετανοέω to perceive afterwards or too late to change one's mind later to repent. Thats from the Liddell and Scott lexicon by the way.
Meta change alter after with + noeoo mind consciousness to think
So repentance is not merely regret and sorrow but an active process of change.
Ἤγγικεν is at hand has drawn near comes closer approaches
Perfect Tense of ἐγγίζω which comes from ἐγγύς an adverb near nigh close coming near
Note the use of the Perfect and not the Imperative or an Aorist Subjunctive.
Change your mind for heaven has been and is coming closer!
Notice also sin is not mentioned just the importance of change?