As with other Christians, faith plays a crucial role in both the beliefs and practices of members of The Church of Jesus Christ of Latter-day Saints, Mormons. The Book of Mormon teaches
no unclean thing can enter into [the Father's] kingdom; therefore nothing entereth into his rest save it be those who have washed their garments in my blood, because of their faith, and the repentance of all their sins, and their faithfulness unto the end." (3 Nephi 27:19)
What can we say about that faithfulness until the end? The 20th-century French thinker, Paul Ricouer defines faith in terms of these synonyms for that term ("Le soi dans le miroir des Ecritures," Amour et justice 52-53):
"A feeling of absolute dependence" in relation to a creation that precedes me
"An ultimate concern" at the horizon of all my preoccupations
"Unconditional trust" that hopes in spite of everything
And Ricoeur points out that, however we formulate what we mean by the word, we can't reduce its meaning to speech or writing because faith is the bedrock on which we build our understanding of things rather than the product of that understanding or a component within it.
The bedrock status of faith doesn't make it something we cannot talk about reasonably. It means that our talk about it will always remain about it, circling it, rather than ever getting right to it. However, though Ricoeur and others can help us see the depth of meaning that we may find in the word faith, the best source for thinking about what faith means is scripture.
A glance at biblical Hebrew, in which the word "faith" usually translates the word group amn, shows that for biblical writers faith is a way of being rather than a truth-content (or the absence of a truth-content). To be faithful is to be established and firm. It is to have fidelity to God, to be trusting of him in the ways revealed through scripture.
In the New Testament, the Greek word that most often stands behind the English translation "faith" is pistis. Since the early Christian Church began from within Judaism, it is no surprise that those using that Greek word also appear to understand it as something other than a truth-content.
Like faith in the Hebrew Bible, New Testament faith is an act. It is something a person does more than it is a belief-content that she holds. Faith is an act of trusting. So to have the faith required of Jesus' followers is to be trusting of God and the call that he makes through scripture and his prophets.
Do Mormons have a unique take on faith? In some ways yes, but in most ways no.
Unlike Jews and other Christians, we believe that one of the reasons we can put our trust in God and be faithful to him is that he is "the literal Father of our spirits" (e.g., Bruce Hafen).
It isn't clear what we mean by that phrase, but at the very least we don't take his fatherhood to be metaphorical. It also isn't clear how our spiritual existence came about. Nevertheless, it is clear that there is some fundamental sense in which the Father and we are "of the same species" as Mormons often say. (I have some objections to that language, but they are not important to my point here.) We can trust him because he is like us and we will be like him (1 Jn. 3:2).
Like other Christians, we believe that God is a being we can trust because, as our Father, he loves us and wants the best for us. He wants us to return to him, and he has provided the means by which we can do so.
We use different names for that means. Sometimes we call it "the plan of redemption" (e.g., Alma 12:25). Sometimes we refer to it as "the plan of salvation" (Alma 42:5) or "the great plan of happiness" (e.g., Alma 42:8). Whatever the language we use, the point is that our Heavenly Father desires for us to be with him.
Faith also means that we understand his commandments as the advice and explanations of a loving Parent telling his children what they must do to be live ultimately happy lives, the kind of life he lives.