An interesting papal statement to the effect that failure to recognise the existence of God is a sin. It might seem obvious: but both Rahner and Maritain in their different ways countenanced the idea of ‘anonymous theism’, where people really believe in God even though they think that they don’t, and whose atheism is therefore not a sin.

If, then, human beings with their intelligence fail to recognise God as Creator of all, it is not because they lack the means to do so, but because their free will and their sinfulness place an impediment in the way (Fides et Ratio, 19)

Si porro intellectu suo non eo usque advenit homo ut Deum omnium Conditorem cognoscat, hoc non tam deficienti instrumento est tribuendum, quantum potius impedimento libera ipsius voluntate ac peccatis propriis interiecto.