Charles H. Spurgeon on Psalms 78:33

Therefore their days did he consume in vanity. Apart from faith life is vanity. To wander up and down in the wilderness was a vain thing indeed, when unbelief had shut them out of the promised land. It was meet that those who would not live to answer the divine purpose by believing and obeying their God should be made to live to no purpose, and to die before their time, unsatisfied, unblessed. Those who wasted their days in sin had little cause to wonder when the Lord cut short their lives, and sware that they should never enter the rest which they had despised. And their years in trouble. Weary marches were their trouble, and to come to no resting place was their vanity. Innumerable graves were left all along the track of Israel, and if any ask, "Who slew all these?" the answer must be, "They could not enter in because of unbelief." Doubtless much of the vexation and failure of many lives results from their being sapped by unbelief, and honeycombed by evil passions. None live so fruitlessly and so wretchedly as those who allow sense and sight to override faith, and their reason and appetite to domineer over their fear of God. Our days go fast enough according to the ordinary lapse of time, but the Lord can make them rust away at a bitterer rate, till we feel as if sorrow actually ate out the heart of our life, and like a canker devoured our existence. Such was the punishment of rebellious Israel, the Lord grant it may not be ours.