Adam Clarke on Hebrews 6:15

He obtained the promise - Isaac was supernaturally born; and in his birth God began to fulfill the promise: while he lived, he saw a provision made for the multiplication of his seed; and, having continued steadfast in the faith, he received the end of all the promises in the enjoyment of an eternal glory. And the inference from this is: If we believe and prove faithful unto death, we shall also inherit the promises; and this is what is implied in the apostle's exhortation, Heb 6:12 : Be not slothful, but followers of them, etc.