In the OT the hardening of the heart is ascribed both to the individual (Pharaoh in Exod. 8: 15) and also to God's action on the individual (Exod. 10: 1). Paul takes up the latter in Rom. 9: 18 as part of the sovereignty of God which is not arbitrary or unjust. In the gospels (e.g. Mark 6: 52) the disciples' failure to understand the significance of Jesus' miracles is ascribed to ‘hardness’ or stubbornness.