Isaac had been trained up in a believing dependence upon the Divine grant of the land of Canaan to him and his heirs; and now that there is a famine in the land, Isaac still cleaves to the covenant. The real worth of God's promises cannot be lessened to a believer by any cross providences that may befall him.
If God engage to be with us, and we are where he would have us to be, nothing but our own unbelief and distrust can prevent our comfort. The obedience of Abraham to the Divine command, was evidence of that faith, whereby, as a sinner, he was justified before God, and the effect of that love whereby true faith works.
God testifies that he approved this obedience, to encourage others, especially Isaac.