Adam Clarke on Genesis 22:8

My son, God will provide himself a lamb - Here we find the same obedient unshaken faith for which this pattern of practical piety was ever remarkable. But we must not suppose that this was the language merely of faith and obedience; the patriarch spoke prophetically, and referred to that Lamb of God which He had provided for himself, who in the fullness of time should take away the sin of the world, and of whom Isaac was a most expressive type. All the other lambs which had been offered from the foundation of the world had been such as Men chose and Men offered; but This was the Lamb which God had provided - emphatically, The Lamb Of God.