"As we will see when we look at galdor or charms in Old English literature, the function of the spoken verse charm is intended to control and direct the raw potency of the healing materials (whether animal, vegetable or mineral). We may imagine that the natural properties are rather like a scattergun, and they need to be aimed and channeled very carefully in order to be sure of hitting the target. The charm performs this function.
In fact, in some senses, speech during a ritual is critical to the success of the operation and, since speech is an incorporating act - it establishes a channel of communication between speaker and hearer - it must be carefully controlled. Some rituals specify that certain parts must be performed in silence, presumably because speaking will dissipate or misdirect the healer's control over the powers he expects to release.
An alternative to speech, language may be written, and a written formula may encompass and preserve the power of the charm and the ritual. Runic characters cut into horn, wood or bone and smeared with the charm-worker's blood, may have allowed better, more precise or more permanent control than mere spoken words.
Runestaves, the characters themselves, allowed communication between the worlds of men and gods, the secular and the sacred; it is likely that runes were used in divination and sortilege as a means of interpreting the flow of events. Runes and charms could both mediate between the inner and outer realms, the home and the wide world.
Charms are well evidenced in the Old English corpus, being mostly either non-religious or of only a vaguely religious character. Prayers do not seem to form part of the tradition outside of the specifically Christian, and mostly Latin, formulas present in the Lagnunga. Charms are potent in themselves, forms of word and deed which unleash power, while prayers are appeals to outside powers for their intervention. Spells are an attempt to bind these powers to the user's will."
— Leechcraft: Early English Charms, Plant Lore, and Healing by Stephen Pollington