According to the traditional spiritual theology of Catholicism, people begin at the level of children spiritually. In fact Saint Paul spoke of this several times, commenting once that the people he was writing were spiritual children and he had to feed them milk instead of solid food. Others go on to what has been considered spiritual adulthood. (Few reach the spiritual maturity of saints.) That means that people have different levels of spiritual maturity. Many live in spiritual childhood. For such people fear of the results of sin may be a normal way of saving themselves from spiritual destruction. Others more mature act often or usually out of love of God. Both motivations are good because since both can lead to salvation, though love of God is a better motivation, for those who have reached that way of living, which only is possible through the grace of God. We should all strive for such spiritual maturity–but all the same, some are spiritual children.
My favorite book providing this theology is the 2 volume “The Three Ages of the Interior Life,” by Reginald Garrigou-Lagrange (Dominican spiritual theologian who in fact was one of Pope John Paul II’s teachers in Rome in the 1940s).