I volunteer at kid's church and at times I also learn with the kids. I may have heard and read the stories countless time but in that same story, there is a new revelation. When God promised Abram to leave his country and people to go to a land that He promised (Genesis 12). Abraham did that, he believed God and left to go to an unknown land. I find this sense of faith, a faith bigger than a mustard seed. Leave all you know and have ever known to an unknown land, uncertain on what lies ahead because of a promise. Faith is to hope for things not seen, rendering them as if they are (my definition). I once heard that the currency of God's kingdom is FAITH, I now see it as seeds planted, patiently waiting for the abundant harvest. No wonder it was counted as righteousness when Abraham believed God. I sometimes wonder because we are from Him, the familiarity of His voice is known to us even though He has not spoken to one before. Now Abraham's harvest was more descendants more than the stars he can count. Abraham's need (lack of a child) was met in abundance not just in descendants but all areas of his life was blessed. And that blessing continued to his descendants.
However, for God's promise to be fulfilled we have a part to play so that it comes to fruition. In the book of Joshua 21:43-45 (the Israelites have arrived in Canaan and settled), God fulfilled His promise to the Israelites. God's promises are not subject to time but they are subject to one's obedience. The faithless generation died (40 years) so that the faithful ones can go and occupy the promised land. Abraham leaving his place was him obeying God. Faith precedes obedience. It seems like promises are like contacts between (in this case) God and man. Just like any contract, both parties have a part to play so that what is to be achieved (promise) can come to pass. The Israelites had to fight for the land to occupy it. God was always with them, He helped them conquer all their enemies. He fulfilled all His promises to the Israelites. God funds His plans. When God promises, we should not only have faith, we should obey (action) Him so that His promises are fulfilled.