Our fathers understood not Thy wonders in Egypt… – Psalm 106:7

They ‘understood not His wonders in Egypt”, because their hearts were hardened by their association with a proud, worldly, idolatrous and yet cultured nation, and they had turned aside from the spiritual faith of their fathers. Wonders were wrought, and they saw them, and were amazed; but they did not see beneath the surface, nor perceive the Lord’s meaning in them. The fact is, dear friends, these people had no deeply spiritual work upon their hearts. Beloved, I pray to God for you who are newly called out from the world, that the first working of grace in your souls may be deep, true, clear, and lasting. I would have you not only know but understand. Depend upon it- a man’s after-character is very much shaped by the mode of his conversion. Why do some turn back altogether? It is because their change of heart was not that thorough radical conversion which involves the creation of a new nature. They felt certain superficial impressions which they mistook for the new birth, and they made a hasty profession which they could not afterwards maintain. They were not thoroughly saved from the dominion of sin, or they would have held on till the end. Many professing Christians of whom we have a good hope that they will prove to be sincere, never had any deep conviction of sin, nor any overwhelming sense of their need of Jesus: hence they have seen little of our Lord in His glorious offices, and all-sufficient sacrifice, and have gained no thorough understanding of His truth…I am afraid for you if you have only a flimsy experience, a skin-deep conviction, a blind man’s apprehension of heavenly light. No wonder if very soon you forgot, and afterwards rebel. Let us pray to God that both in ourselves, and in those whom we bring to Christ, the work of grace may be deep and thorough; and may our faith in Jesus be sustained by a clear understanding of the gospel, and of our Lord’s dealings with us! ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/2204.cfm