What is the nature of the repentance that God commanded in His Book after paying off the remaining balance of my father's usurious loan in one lump sum?

All praise is due to Allah for guiding you, and thank you for advising your father to put his trust in Allah, for whoever trusts in Allah, He is sufficient for him. Allah is the Creator who guides, feeds, quenches thirst, heals, causes death, and gives life. Whoever entrusts his affairs to Him, He suffices him, and whoever fears Him, He grants him a way out and provides for him from where he does not expect. Repentance is accepted for whoever repents, believes, and performs righteous deeds, and Allah transforms their evil deeds into good ones. Repentance involves acknowledging the sin, abandoning it, regretting it, resolving not to return to it, and performing many good deeds. The father must repent from usury, and you must adhere to Allah's straight path and come to know Him in times of ease. Fear Allah in His commands and prohibitions, and beware that He sees you where He has forbidden you. Happiness lies in fearing Allah, and Allah has promised the believing doers of good a good life, and He has warned those who turn away from Him of a constricted life.