The practice of smudging, and it's accompanying sage bundles, abalone shells, and hawk feathers, is familiar to most us who seek peace in the world of spirituality.
Early humanoids probably picked and saved aromatic stems and leaves for their scent or other properties.
Citronella, sage and rosemary were burnt to repel insects by the cave dwellers. It's easy to imagine that the health benefits of burning herbs could transition into a perceived spirituality, as people watched smoke wafting up from the fire, and breathed in the pungent, aromatic scents transforming their space, and their senses in an intangible, ethereal way. Those moments may have moved them into meditative states, bringing them closer to an encounter with the Divine.
Smudging, though, is most associated with northern Native American traditions. Sage is not the only herb used in smudging ceremonies; cedar, tobacco, yarrow and sweetgrass are used as well. The practice is often done to mark the beginning of ceremonies. The clouds of smoke are used to bathe away negative energies and to purify spaces, and people. The herbs, or "medicine" are placed in a shell or fireproof container and lit. A feather or a fan is used to waft the smoke into the air.