And thou saidst, I will surely do thee good. (Genesis 32:12)
This is the sure way of prevailing with the Lord in prayer. We may humbly remind Him of what He has said. Our faithful God will never run back from His word, nor will He leave it unfulfilled; yet He loves to be enquired of by His people and put in mind of His promise. This is refreshing to their memories, reviving to their faith, and renewing to their hope. God’s Word is given, not for His sake, but for ours. His purposes are settled, and He needs nothing to bind Him to His design of doing His people good; but He gives the promise for our strengthening and comfort. Hence He wishes us to plead it and say to Him, “Thou saidst.”
“I will surely do thee good” is just the essence of all the Lord’s gracious sayings, Lay a special stress on the word surely. He will do us good, real good, tasting good, only good, every good. He will make us good, and this is to do us good in the very highest degree. He will treat us as He does his saints while we are here, and that is good. He will soon take us to be with Jesus and all His chosen, and that is supremely good. With this promise in our hearts we need not fear angry Esau or anyone else. If the Lord will do us good, who can do us hurt?
C.H. Spurgeon, Faith’s Checkbook