Gen. 16:10-11 God hears Hagar.

What a comforting message we have here.  There was a problem with Hagar and Sarah.  in v.9  God tells Hagar to go back to Sarah. Hagar was having trouble with Sarah. She did go back because now she knew God's will.  It appears Sarah was the problem.  We may have to be around people who don't like us in order to accomplish God's will.  Especially in the work place.  Hagar went back.  She was blessed with favor and good things come our way when we are in God's will.  Moses hung out with a people who wanted to stone him--his own people.  Mercy is a great thing as we live around those who don't like us.  God gives us more attention in those times to comfort and bless us. 
I have experienced this myself. Never knew so many people were standing with me in my hard times. it is all grace. It was when things were going wrong that I found how much they cared. He brought them out of the closet so to speak. The steps of the righteous are ordered of the Lord--even if they make mistakes. He keeps us on track.

Gen. 15:8-9 how shall we know?

We see a  real picture of our full redemption here.  Also the quarantee.  It all starts with a question.  Abraham says How shall I know?  Notice that God already revealed that he will give him the full inheritance.  The bible shows us that also.  see Eph. 1:14  ---- Col.1:12----  Col. 3:24--- Heb. 9:15---
in Col.1:12  the word partakers there means associates. We are joined together with Jesus to be receivers of our inheritance.
What is the answer to so many questions that come God's way to receiving from him his wonderful promises. v.9  The answer is a covenant made through sacrifice.  In our case it is Jesus the Lamb. He can pay no more for it is paid in full. Jesus said on the cross it is finished.  The word salvation means the total supply of every need.  it is used many times in the bible . Not just being born again but any blessing God gave. David says it often in the Psalms. The bottom line is Abraham did receive the promise of the land and so did Israel. We have that seed who is Jesus.

Gen. 15:5 innumerable grace

God is tremendous in numbers.  In Heb.12:22  we have the angels are innumerable.  In Heb. 11:12 stars and sand are the same.  If we look around us we see many things in a innumerable  amount. One of the attributes of God speaks of all sufficiency. That would ammount to innumerable sufficiency.  He has forgiven us from innumerable sins.  That is innumerable grace.  We have many enemies. darkness and light don't get along. We must manifest light towards the darkness.  God has promised to be that light.  Through Jesus we have all the light we need to overcome and be victorious.  We must throw out the lying thoughts the enemy place in the mind by casting them down as vain imaginations.  They may come but we confess that is not my life only a passing lying thought planted by the evil one. Remember God looks on the heart not the thoughts--the devil can plant thoughts. We just reject them and say I live by Jesus now.
Yes al that does fit in ith the passage.  We are the seed of Abraham--read Gal.3: all.  We are the innumerable seed--one of them.  We have innumerable graces to help us stay as one of those seeds.
We see disasters around us. They do innumerable damage. When the walls of Jericho fell down , that was a big damage that shows how big the power of God is.  That is a grace of protection that we desire. Looks like the enemy has the upper hand.  It took the hands of one man Samson to pull the pillars of the temple down.  But just think we raise our hands in praise to God and he pulls down strongholds. We are full of God's grace and innumerable love. God fights for us through our praise.