Noah was basing his whole life and decisions on something unseen… on a God who is unseen, who warned him about an unseen flood. Why else would Noah build an 8,000 ton ship on dry land and spend almost 100 years doing so? Only because he believed in an unseen God and believed His Word was true. The writer of Hebrews is saying to us that this better be us, because this is the way of a man who is right with God. God has spoken and in faith you rest your whole life upon that.