Hebrews 11
17By faith Abraham, when he was tested, offered up Isaac on the altar. He who had received the promises was ready to offer his one and only son,
c 18even though God had said to him, “Through Isaac your offspring will be reckoned.”
d 19Abraham reasoned that God could raise the dead, and in a sense, he did receive Isaac back from death.
Abraham received the promises of God's word which included, "Through Isaac your offspring will be reckoned." So, he reasoned that Gjod could raise the dead, considering God's instruction that he offer his son upon the altar.
That action displayed his faith in God's word, rather than faith in the work (which by any other circumstance, human sacrifice is strictly forbidden in the law). So, God's word preceded Abraham's faith in God to fulfill His promises. In other words, God gave His word to Abraham and Abraham believed it.
And there is no one that God hasn't given His word to.