**Some practictioners of magic claim that magic is simply a focused inner force. Basically you believe something so much that it happens. Some practictioners of magic rely on visualization. **
There are some kinds of magic that can be based on nothing more than focused personal power. However, there’s no magical theory that says ‘believe enough and it will happen’. Faith, itself, is not considered a cause of anything in magical art, though faith is helpful in encouraging confidence and concentration. Even when magic relies entirely on personal power it always involves technique - visualization, channeling of energy, etc. It is the personal will that makes magic work.
This is one of the reasons that some kinds of religion dislike magic. Many systems teach that only the will of their One God is supposed to matter in the world, and that efforts by individuals to make their own will happen are at least risky and at worst pridefully sinful.
Historically, most systems of magic depend on alliance between humans and a variety of spirits, from local nature beings all the way to the Deities. This involvement with non-biblically-approved spirits is a major source of the dislike of both old and new testament writers toward the practice.
Many sorts of monotheistic magic have been composed, in which the entire source of spiritual power is the biblical God, or which ally humans with various ‘angels’ and other spiritual servants of the Highest. The Roman church vassialted on this sort of magic over the centuries - I’m far from sure there aren’t people in the religious life today doing mysticism and even ritual magic based on renaissance christian magical forms. Nonetheless most sects of christianity reject anything that smells of using personal will to make specific alliances with spirits, or manipulate specific impersonal spiritual powers.