For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek. – Romans 1:16

The gospel is to the true believer a thing of power. It is Christ the power of God. Ay, there is a power in God’s gospel beyond all description. Once, I, like Mazeppa, bound on the wild horse of my lust, bound hand and foot, incapable of resistance, was galloping on with hell’s wolves behind me, howling for my body and my soul, as their just and lawful prey. There came a mighty hand which stopped that wild horse, cut my bands, set me down, and brought me into liberty. Is there power, sir? Ay, there is power, and he who has felt it must acknowledge it. There was a time when I lived in the strong old castle of my sins, and rested in my works. There came a trumpeter to the door, and bade me open it. I with anger chide Him from the porch, and said He ne’er should enter. There came a goodly personage, with loving countenance; His hands were marked with scars, where nails were driven, and His feet had nail-prints too; He lifted up His cross, using it as a hammer; at the first blow the gate of my prejudice shook; at the second it trembled more; at the third down it fell, and in He came; and He said, “Arise, and stand upon thy feet, for I have loved thee with an everlasting love.” A thing of power! Ah! it is a thing of power. I have felt it here, in this heart; I have the witness of the Spirit within, and know it is a thing of might, because it has conquered me; it has bowed me down.

“His free grace alone, from the first to the last,
Hath won my affection, and held my soul fast.”

~ C.H. Spurgeon

http://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0007.cfm