Crusaders increases it's Attack points by 3 when any Holy card is on the opponent's field. If there are no applicable cards on the board, the ability will not activate unless one is added. These points will not carry over to subsequent rounds.
The Crusades were a series of religious wars sanctioned by the Roman Catholic Church in the medieval period with the aim of recovering the Holy Land from Islamic rule. The term is also applied to other campaigns fought to combat paganism and heresy or to resolve conflict among rival groups, or to gain political or territorial advantage.