Including abalone shells in your smudging rituals means you are incorporating all four of the earth's elements: the shell represents water, the smoke represents the air, the unlit herbs or sticks represent earth and once they're lit they represent fire. By incorporating the elements into your smudging ritual you're inviting mother earth to be the focus of your ceremony. It is here that transformations and manifestations have room to occur.
Light smudge sticks or loose leaves, wait a moment, then blow out flames. Rest the sticks in the abalone shell, using it to collect ashes or embers.