What is true faith?
A. True faith is not only a certain knowledge, whereby I hold for truth all that God has revealed to us in His Word, but also an assured confidence, which the Holy Ghost works by the gospel in my heart; that not only to others, but to me also, remission of sin, everlasting righteousness, and salvation are freely given by God, merely of grace, only for the sake of Christ’s merits. Heidelberg Catechism Lord’s Day 7.
Faith is also the bond uniting us to Christ by our being grafted into him. Picture of grafted vine.