Faith is a stat in Demon's Souls. Raising it increases miracle power (Miracle Power=Faith x 100), magic defense (slightly more than other stats), damage for Blessed weapons, Istarelle, the Meat Cleaver, and the Large Sword of Moonlight, and available miracle memory (max of 4 memory slots).
The player needs at least 10 Faith to learn miracles from the Disciple of God or Saint Urbain. If the player speaks to the Worshipper of God with at least 20 Faith, and before Saint Urbain arrives in the Nexus, she will believe the player can hear the voice of God and give them a Pure Faintstone.
Memory Slots TableStats are sourced from Atlus's Official Demon's Souls Guide.