Hebrews 6

Paul provided an interesting analogy as he wrote first -

"...we desire that every one of you do shew the same diligence to the full assurance of hope unto the end:
12 That ye be not slothful, but followers of them who through faith and patience inherit the promises."  (New Testament | Hebrews 6:11 - 12)

To me, Paul is suggesting that we pursue, in all diligence, to keep the commandments and serve the Lord  with a sustaining hope that His promises are secure for Paul then compares -

"For when God made promise to Abraham, because he could swear by no greater, he sware by himself,
14 Saying, Surely blessing I will bless thee, and multiplying I will multiply thee.
15 And so, after he had patiently endured, he obtained the promise."  (New Testament | Hebrews 6:13 - 15)

I believe Paul is teaching that the Lord Himself covenanted with Abraham the promise of a great, righteous posterity.  After a 100 years, Abraham could have lost all patience, hope, and faith.  But he didn't.  He endured and eventually at the least expected time, he obtained the promise of Isaac.

When we make covenants and receive the promise of the Lord, we must move forward in faith and the full assurance of hope that we shall obtain the promise.