40 By the very fact, therefore, that the faithful with sincere mind give such consent, they open up for themselves a treasure of sacramental grace from which they draw supernatural power for the fulfilling of their rights and duties faithfully, holily, perseveringly even unto death. Hence this sacrament not only increases sanctifying grace, the permanent principle of the supernatural life, in those who, as the expression is, place no obstacle ( obex ) in its way, but also adds particular gifts, dispositions, seeds of grace, by elevating and perfecting the natural powers. By these gifts the parties are assisted not only in understanding, but in knowing intimately, in adhering to firmly, in willing effectively, and in successfully putting into practice, those things which pertain to the marriage state, its aims and duties, giving them in fine right to the actual assistance of grace, whensoever they need it for fulfilling the duties of their state.
Source: Casti Connubii (Vatican.va)