O YHWH, why do you make us wander from your ways and harden our heart, so that we fear you not? Return for the sake of your servants, the tribes of your heritage.
Isaiah 63:17

God hardens the hearts of his people so that they would believe a lie. If you don't believe that, just look around you! Turn on the evening news for a few minutes. It's all lies, and so many people believe it. This is for his own purposes and for the ultimate good of his Kingdom. Our job is to have faith, to be faithful, and to do the best we can with what we are given.