For it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God— not by works, so that no one can boast. ~ Ephesians 2:8-9 NIV
Faith is a powerful thing. It is a miraculous thing. It is the hopeful belief in something that is beyond us for good or for ill.
Many people in the Bible demonstrated faith. You know people in your own life that no doubt demonstrate faith in something, even if it is something not altogether worthy of being a recipient of their faith. God is always a worthy recipient of our faith.
It is a simple acknowledgement placing your faith in God. It means developing a hopeful belief that He will, can, and has provided an alternative to your sinful nature. It is this faith at work in us that, when combined by the extended grace of God, ushers us into salvation.
Some would teach that you can only be saved by showing some outward sign, perhaps baptism, or the demonstration of some spiritual gift. It is my belief, and the clear point of this passage in Ephesians 2, that the only condition for salvation is faith. Simply put, you must acknowledge and want God alone as the source, recipient, and channel for your belief.
Faith is a many-faceted thing. It creates a mountain of possibilities in our lives, but its principle purpose is straight forward. Faith is the Holy Spirit working in our heart, mind, soul, and strength in a way that empowers us to trust in God beyond our own means. Grace alone from God received by Faith alone. That is salvation at work in us.