[Solution]The passage in Hebrews that quotes/alludes to the OT.

The next phrase of Hebrews 11:17 reads “It was he [Abraham] to whom it was said, ‘IN ISAAC YOUR DESCENDANTS SHALL BE CALLED.’” This is an allusion to Genesis 21:12 where God promises Abram (later called Abraham) that through his son Isaac “your descendants shall be named.” The following verse states “And he [Abraham] considered that God is able even to raise people from the dead…” Here we can deduct that what prompted this belief on Abraham’s part must have been something mentioned previously–namely God’s promise of descendants through Sarah and her son Isaac (Genesis 17:15-21). Through these events–the divine promise and subsequent testing–Abraham learned that nothing is impossible for our faithful and mighty Lord!

Finally Hebrews 11:19 declares “He [Abraham], having waited long endured, obtained [the promise].” Once again this phrase reflects back upon Genesis 15 which speaks of how after many years of waiting for a child of promise (Isaac), obediently enduring hardships along the way and trusting in His covenant relationship with Yahweh–God fulfilled His word and granted Abraham a miracle!

In conclusion then we see how throughout this passage in Hebrews there are numerous references made back not only to specific verses within Scripture but also concerning certain key aspects such as testing of obedience/faithfulness encountered by believers; miracles performed by God; assurance given as well as eventual fulfillment Himself etc. It is therefore clear why Paul would make particular use of these themes throughout his letters –for they truly speak volumes about whom our Lord really is!