There has always been the question as to the possibility of a person stepping over a line — that is, sinking so low in sin that the grace of God cannot reach him. While I do not believe that you could ever get to a place where God by His grace could not save you, I do believe that if you persist in rejecting God's grace and mercy, the day will come when you will step over that line. This does not mean the grace of God cannot reach you, but it does mean that there will be nothing in you that the grace of God can lay hold of.
Let me illustrate this with the story of a man I met when I first came to California as a pastor in 1940. His wife wanted me to visit him in his home because he was sick and dying. She asked me to present the gospel to him, and I did. He was a very polite man, and he listened to me. Then he said to me, "I would say, 'Yes, I will accept Christ as my Savior' — in fact, I am going to do it. But I want to tell you this: I have played and trifled with God all my life. I have been down to an altar twenty-five times. I have made promises to Him and then turned from Him, and I have never been sincere. Honestly, I cannot tell you right now whether I am sincere or not." All I could do at his funeral as I looked down at him was to say under my breath, "Oh, God, I hope he was sincere. I hope he really meant it. I hope Your grace reached down and touched him."
You can trifle with God too long. The nation Israel did, and the day came when God said, "I will no longer have mercy on you."
But I will have mercy upon the house of Judah, and will save them by the Lord their God, and will not save them by bow, nor by sword, nor by battle, by horses, nor by horsemen. (Hosea 1:7)
"However," God said, "I am not ready yet to judge the house of Judah." Why will He spare Judah and not Israel? For the sake of David. God had said that for the sake of David He would not divide the kingdom under the rule of Solomon. Again and again He said that for the sake of David He would save the southern kingdom. Someone may want to criticize this and say that it is not fair. I don't know whether it is fair or not, but I thank God that He showed mercy to me, that He was patient and continued to show mercy, and that He continues to do so even today.
—From Edited Messages on Hosea by J. Vernon McGee