Garrigou-Lagrange

This explains why we must always pray. The necessity of prayer is founded on the necessity of actual grace. Except for the first grace, which is gratuitously given to us without our praying for it, since it is the very principle of prayer, it is a thoroughly established truth that prayer is the normal, efficacious, and universal means by which God wishes that we should obtain all the actual graces we need.

- Reginald Garrigou-Lagrange, The Three Ages of the Interior Life. Vol.1. (St.Louis:Herder Book, 1947), #.

Further elucidation of the concept of actual grace and its necessity in the life of grace of the soul.