"I believe the ONLY reason a person perseveres is simply because God has transformed them so they will perform good works. It goes back to Augustine's interpretation of Ezekiel 36 where God states that He will put a new heart in us and cause us to walk in His statues."
One of the holy hermits of the Egyptian desert in the 4th century was a black monk named Abba Moses the Lybian. Even during his lifetime he was renowned for his holiness and his wisdom in matters of theosis. In his opinion, "The strength of those who wish to acquire the virtues is as follows: if they fall, let them not lose their courage, but let them be sure to make a new beginning at their endeavor. Insofar, then, as we put all our energy into practicing the virtues, let us await the Lord, showing Him a generous resolve and calling on His aid, and without fail He will strengthen us with His mercy and bestow His Grace on us in abundance, in which case we will accomplish every good easily and without exertion."