Adam Clarke comments that the word "it" in "it is the gift of God" can be more accurately translated "this." But "it" and "faith" are of different genders. In the Greek language, as in many others, the gender of the pronoun has to match the gender of its antecedent. The antecedent, then, cannot possibly be "faith" because "it" is neuter and "faith" is feminine. "It" must refer to another neuter word, the word "saved." Faith indeed is a gift of God, but it cannot be proved so by this verse.
Faith is produced by the grace of God given to us. God's grace empowers us to believe. The power to believe and the act of believing are two very different things. Without the power to believe, no one has ever believed with the kind of belief that is necessary for salvation, but once a person has that power, once he is enabled, once the grace, the gift, has been given to him, then the act of faith is the person's own.
John W. Ritenbaugh
Faith (Part 5)