God's grace is offensive. By nature we do not want God to be gracious to us because it offends us.
Now, it might sound a bit odd to say that, so let me explain. We are by nature proud. Because of this we do not naturally delight in the idea that salvation must be by grace alone. Why? Because that means that all the glory goes to God alone, and we want to take some of that glory for ourselves. We want to be able to contribute something to our salvation, so that we can be honoured. In effect we want to rob God of the praise that is rightfully His. Charles Spurgeon in a sermon from Isaiah 55:1 says:
Pride is woven into man’s nature. The prodigal became a prodigal through his love of independence, he desired his own portion of goods to do as he liked with. After he became a prodigal his time was occupied with spending — he spent his money riotously; he loved to play the fine gentleman and spend. Even when the prodigal came to himself the old idea of paying was still to him, and he desired to be a hired servant, so that if he could not pay in money he would pay in labor.
We do not like to be saved by charity, and so to have no corner in which to sit and boast. We long to make provision for a little self-congratulation. You insult a moral man if you tell him that he must be saved in the same way as a thief or a murderer, yet this is no more than the truth. For a woman of purity to be told that the same grace which saved a Magdalene is necessary for her salvation is so humbling, that her indignation is roused, and yet it is the fact, for in every case salvation is “without money and without price."
