Are sacraments efficacious even if not understood by the one receiving them? Doesn’t grace require active cooperation of faith, knowledge, and will?

When a sacrament gives us a grace requiring cooperation, such as the grace to love our spouses, it does require us to cooperate for that grace to manifest itself. But when a sacrament gives us a grace that does not require action (such as sanctifying grace), then our active cooperation is not required. This is not to say that our passive cooperation is not needed. Sacraments communicate their grace to us unless we put obstacles in the way--but we can put obstacles in the way.

For example, in order to receive the sacrament of matrimony, it is necessary to be open to the essential properties of marriage, such as unity and indissolubility. If, at the time the marriage is contracted, one party is not open to the essential properties, the marriage will not be valid. There will be no real marriage at all.

The Code of Canon Law says, “But if either or both parties through a positive act of the will should exclude marriage itself, some essential element, or an essential property of marriage, it is invalidly contracted” (CIC 1102:2). But “error concerning the unity, indissolubility, or sacramental dignity of matrimony does not vitiate matrimonial consent so long as it does not determine the will” (CIC 1099).