Lexically: Faith is related to assent, acceptance, and acknowledgment.
Technically: Its object is the religion authentically brought from Allah by the Messenger ﷺ.
Heart and tongue: Inner assent and outward profession are related but distinguishable for theological and legal purposes.
Actions: Their religious obligation is clear, while schools differ in how they enter the technical definition of faith.
A sincere religious life unites recognition of truth, inward acceptance, and fulfillment of divine commands. The scholarly distinctions identify the different roles of definition, outward evidence, duty, and perfection without severing that connection.
The next discussion of the increase or decrease of faith builds on these foundations.