Faith is therefore not a simple act of understanding (an acceptance-as-true) or of the will (trust) or of feeling; it is rather a life-project that lays hold of all these powers and includes them, and a comprehensive mode of existing. Faith is at the same time an act (fides qua creditur) and a content (fides quae creditur). Faith is the comprehensive re-action of the human being to the prior action of God in revealing himself; it is trusting in God and a building on God, a gaining a foothold in God, a saying of ‘Amen’ to God, with all the consequences this entails. To have faith is to take God seriously as God, without reservations; it is to give him the honour and to glorify him as Lord; it is to acknowledge his lordship with praise and thanksgiving.
Walter Kasper, The God of Jesus Christ (New York: Crossroad, 1984), 122.