Feuerbach's philosophy has been described as a form of "materialism," but in my view that term is applicable only in the sense that he rejects traditional spiritual or religious beliefs. In The Essence of Christianity, he seems to identify religion as a projection of man's awareness of himself, not awareness in an individual or limited sense but a consciousness his own nature as "infinite."
Feuerbach asserts that what distinguishes humanity from the animals is that people have a "twofold" life—a distinct inner and an outer one—while in animals, the inner and outer life are the same thing. Man has an awareness of himself as a type of being (a species), while the animals do not. Though it may, by modern standards, seem unscientific and presumptuous for Feuerbach to assert that he knows what animals can think or not think, this defect doesn't really invalidate the point he is trying to make. He goes on to say that this special quality of people's awareness of themselves as extending beyond their limited, finite selves is the reason for, and the object of, religion.
In my opinion, this is actually easier to understand than most concepts in the writings of major philosophers, and Feuerbach states it with such lucidity that there's little doubt about what he means. In a way, it conforms to a generally secular perspective and, at the same time, the spiritual ideas of many people today who don't espouse traditional religions. God, in Feuerbach's view, is a kind of extension into the "infinite" of man's concept of himself. Thus, as in the sentence you've quoted, religion and the belief in God are forms of man's self-awareness or self-knowledge.
Feuerbach uses an interesting analogy in which he states that the sun, though it is the "object" of all the planets in the solar system, means a different thing, or is a different thing, to each one:
Each planet has its own sun. The sun that illuminates and warms Uranus in its way doesn't have a physical (but only an astronomical or scientific) existence for Earth; and the sun shines not only differently, but actually is a different sun on Earth than it is on Uranus.
His statement seems, at least to me, to relate to philosophical idealism such as Kant's about the outer world, as we perceive it, being a creation of our minds separate from the "thing in itself" or objective reality. In describing the solar system, Feuerbach regards the sun as an object of each planet's separate nature or its knowledge. It's therefore an analogue to religion, or to our concept of God, as an "indirect form of self-knowledge."