Crusaders are part of the clergy of a church and will receive support and training from the church to support their holy duty. They can carry multiple blessings at the same time (where normal mortals can only carry one blessing), they can bless themselves at shrines without the help of a priest and some have access to certain (some would say "forbidden") techniques that they can use to battle other faiths. Their powers are a form of divine magic and comes from their interaction with the forces of Gods .
Crusaders are not necessarily priests although they can be. Some people would even say that the methods of the crusader are at odds with the methods of a priest. Where priests gather and redistribute the divine worshipping powers of a community amongst that community, a crusader gather such power and gives it to himself in order to fight some holy enemy.
Crusaders are not always warriors though and many crusaders don't even own weapons and armour and will never see battle. Their crusade might manifests in the creation of beautiful art, or elegantly written software code, constantly being blessed by the community to fuel their passion and inspiration with divine power. Or they might wage a crusade on ignorance, their weapon being the methods of science and their armour a healthy scepticism, being in a state of constant concentration and heightened awareness so they can spot the most hidden of herbs, bugs in code, minerals or lifeforms in their endless quest to understand the world.
Crusaders are never "crusaders" alone. They are always a "warrior crusader" an "hacker crusader" an "artist crusader" or any other profession. The crusader part of their profession simply underlines the fact that the fruits of their labour are both enhanced by and intended for the divine mandate.
Crusaders are rarely alone either. Their holy quest often demands that a community of worshippers and priests forgoes their regular blessings and instead uses those blessings to create one highly specialized and blessed being. This often makes them a sort of "champion" or "figurehead" of the community. Quite literally the group puts their faith for greatness of the community in a single person.
Weaving multiple blessings
The very fabric of reality is distorted when a person is blessed. When a priest bestows a blessing he removes one blessing before placing the next because multiple blessings could rupture the very reality asunder and kill the person receiving the blessing.
Crusaders are taught how to weave multiple blessings in such an intricate and complex pattern that they overlap without interacting with each other. In essence they are taught how to carry multiple blessings at one time.
Where this process comes natural for most divine beings of even a low ranks, it requires extensive training and concentration to be completed by a mortal and it becomes exponentially more difficult the more blessings are present. Most crusaders in training never actually finish weaving two blessings and thus either die trying or don't become crusaders in the end. Other crusaders sometimes even succeed in successfully weaving three blessings, but so far no known mortal has ever succeeded in weaving four blessings at the same time even though certain high ranking deamons and angels do this by rote.
Unweaving multible blessings; the dangerous ceremonies of the crusaders
Being a crusader and carrying multible blessings is a feat originally taught to mortals by the gods, in the same sense that that gods trained the first priests . But the original crusaders and the many generations of crusaders that came after have found other uses for this knowledge.
Most of these crusader ceremonies use the violent and unstable nature of multible blessings woven into a pattern to deliberate transfer their own blessings unto some subject or victim before unweaving them.
The destruction of altars
An altar is normally protected by divine energies and cannot be destroyed (or even moved) by conventional ways unless with considerable material force. By unweaving their blessings just "in between" the altar and the divine realm it is orientated towards crusaders are able to sever the link with the divine realm, robbing the altar of it's influx of divine protection. This process is called "blighting an altar" and unless a priest fixes the alter with a ceremony of absolving afterwards the altar will be lost within a week or two. After being blighted for about two hours though the altar will be venerable enough for another(!) unweaving ceremony, this time directed directly at the altar itself. This process is called "nullifying an altar" and uses the previous created vulnerability to completely destroy the Altar before a rival priest has a chance to absolve the blight.
The destruction of divine beings
Although any creature can simply grab any weapon and pummel a material divine being until it's husk dies, this does not destroy the actual divine being. When a divine being is decapitated the body tends to "explode" or melt away in seconds and this gives the being time to escape to the divine realms or into a new body already prepared and awaiting animation. Most if not all divine beings even have the ability to kill their own bodies within seconds to escape hopeless situations and try again at a later time in a new body.
Capturing and torturing a divine being is, under normal circumstances, utterly impossible.
Crusaders have found a way to transfer their own blessings into the link in between the divine being and it's material body, effectively strengthening(!) the being it's hold on the body but also rendering it unable to let go, trapping the divine being until such a time that the body dies of natural causes.
Specialized crusaders called "deamon hunters" and "angel hunters" have trained themselves to touch divine beings during combat or during summoning ceremonies while performing this feat. If afterwards the being is netted or even rendered unconscious you can shackle the divine being with material chains.
Strong divine beings can absolve a few of such blessings weaved into their pattern instantly which means that several crusaders might be needed to touch the divine being during combat before it can be successfully bound.
After a divine being has been successfully bound and subdued it can be tortured and questioned. But some crusaders have taken this ceremony even further and with the help of expensive components have found ways of utterly destroying the deamon or angel. This process entails transferring at least three blessings trough the body, "up" the link and into the angel or deamon itself. After the blessing has been transferred it can be slowly but violently unwoven. This process warps reality around the divine being and effectively and painfully erases it's very essence.
This process takes mere minutes with weaker divine beings but could take hours or even days with the strong divine. All the while the deamon or angel needs to remain bound (which might entail several re-bindings) both physically and spiritually.
Most crusaders would also make sure they perform ceremonies that block the divine being from performing ceremonies of it's own that could send a signal to the divine realms as a call for help.
Wise crusaders attempting any of this make sure they have the backing of rival angels or deamons or even the backing of a rival Deity themselves. Or they would wear masks and distort their voices during both the battle and the ceremony while capturing, torturing or destroying a divine being as even the attempt of such a defiant deed towards a god would almost certainly call for a hasty and powerful revenge of some sort.