…The traditional understanding of a person’s fundamental option is that it can be changed according to concrete acts… More recent theories associated with fundamental option have attempted to separate the fundamental option from a person’s acts…
…Some contemporary theologians deny that an individual act, even though it involves grave matter, full knowledge, and free consent (i.e., mortal sin), can separate man from God. In other words, they say that man’s fundamental option is not eradicated by individual sins, no matter how grave, even when done willingly and with full knowledge of this gravity.
As Pope John Paul II notes, “According to these theologians, mortal sin, which separates man from God, only exists in the rejection of God, carried out at a level of freedom which is neither to be identified with an act of choice nor capable of becoming the object of conscious awareness” (Veritatis Splendor no. 69).
According to the Church, individual acts of sin have the capacity to reorient the person, effectively changing the direction of his fundamental option. Venial sin that is not repented of can slowly lead a person to mortal sin (Catechism, no. 1863).
Mortal sin (see Catechism, nos. 1857-59) destroys the life of God within us, thus making necessary “a new initiative of God’s mercy and a conversion of heart” (Catechism, no. 1856). While venial sin can slowly reorient us to the point that our fundamental option is altered completely, mortal sin accomplishes this change in one act.