“Fides Qua and Fides Quae”
The expression fides qua means “the faith which believes.” Here faith is saving faith which receives and holds the riches of Christ’s atonement. He has won for us the favor of God through the merits of Christ. He gives this salvation to us through the word and sacrament and we grab it and hold it by faith. This faith is what the theologians call fides qua – the faith which believes. It’s the fides qua which makes you a Christian.
Fides qua without fides quae is emotionalism with all sorts of heartfelt sentiments but no understanding of precisely what Jesus is all about. Fides quae without fides qua is heartless theological abstractions.