Genesis 26:5 Because that Abraham obeyed my voice, and kept my charge, my commandments, my statues, and my laws.
The Lord had just repeated to Isaac the same Promises of the Covenant that He made with Abraham, his father. God promised Isaac seed, land, and blessing. Just like Abraham ”believed God and it was counted to him as righteousness,” so Isaac was given the same heart to receive the Covenant, believe it and obey it.
Abraham did not cause God to make a covenant promise to him because he was obedient. Rather, Abraham obeyed and kept the charge because God called him and promised. The order is important for us: we love Him because He first loved us. The order is not: God loved us because we were good and deserved His grace and blessing. Grace is first; then faith receives the free gift; and then we respond with obedience and good works. God acts in Christ to reconcile the world to Himself; the Holy Spirit creates faith in the heart through the Gospel; the Spirit in the believer moves him or her out of faith to obey.
The faith in the promise of this gospel message stirred Abraham, and Isaac, and us, to obey and keep God’s Word. Why did God choose Abraham and Isaac to bring the “Blessing to all the nations of the earth?” Just grace. Why did God choose me to believe and be saved? Just grace. How I respond to that? With the obedience of faith.