His promises

Psalm 106:24 (Berean Study Bible)

They did not believe His promise.

When we don't trust people we don't trust the promises they make. We start making alternate arrangements and even distancing ourselves from them. Sometimes, that could result in us losing the blessings that the Lord has for us. The Israelites did not believe the Almighty when He promised to deliver the land of Canaan owned by the powerful Canaanites and others. Consequently, that entire generation perished in the wilderness. A promise is only as good as the one who makes it. For a Christian all the biblical promises are backed by the eternal character of God. When we despise His promises we reject Him and harm ourselves eternally.