God had made a promise to Abraham, and Abraham asked God a question; how will I know I will receive it? God gives Abraham instructions - gives him something to do. It's as if God were saying...just keep doing what I tell you to do..keep doing what is right.
We have all gone to a store and gotten back more money than we should have or been undercharged for items, some people mistakenly think this is a blessing from the Lord.
A few weeks ago I purchased some clothing from a store, that I rarely shop at. When I got home and looked at the receipt, I realized I was under charged by $20.
This store is a bit out of the way, I don't pass by it often, and have to make a point of going there. When I saw the receipt and realized what had happened I knew I was going to have to make a trip back to the store..to pay the $20 that I owed.
I've heard many similar stories from believers who say the same type of situation happened to them, and that it was God blessing them. I assure you, this is not God blessing you - this is the test, that always comes before the blessing. God is testing your obedience to see if you can be trusted with the bigger things.
If you don't pass the test, you will have another opportunity to do so...realize it's a test, do the right thing, and then watch for the blessing - Don't blow the blessing!