No just man suffices unto himself for the winning of justification. The divine mercy must always hold out a hand to his footsteps as they falter and almost stumble, and this is so because the weakness of his free will may cause him to lose balance, and if he falls he may perish forever.
John CassianMore John Cassian quotes
The apostles were very sure that everything of theirs which had to do with salvation was a gift to them from God. 'Increase our faith'. They did not presume that the fullness of faith would come to them merely because they freely opted for it. They believed, rather, that it was a gift of God which would have to be granted to them.
John Cassian
... a Christian is quite certain to fall into the same sins which he condemns in another with merciless and inhuman severity, for 'a stern king will fall into misfortunes,' and 'one who stops his ears so as not to hear the weak, shall himself cry, and there shall be none to hear him' (Prov. 13:17; 21:13).
John Cassian