It is evident that one who would merely aim at avoiding mortal sin would not be living according to the standard of moral conduct outlined in the Gospel. Our Lord proposes to us as the ideal of holiness the very perfection of Our Heavenly Father: "Be ye therefore perfect, as also your heavenly Father is perfect." Hence, all having God for their Father must approach this divine perfection - which evidently cannot be accomplished without progress.
--St. Teresa of Avila
