D. James Kennedy, Evangelism Explosion, 3rd edition, p. 101
Imagine that you are out in the middle of a lake and there are two rowboats and you are standing with one foot in each boat. One boat, however, is filled with holes and is sinking fast. It is obvious that unless you do something you will soon be in the lake. The boat with the holes represents ourselves with all of the leaks caused by sin. The boat without holes represents Christ. It should be obvious that with one foot in each boat we shall end up in the same place that we would have ended up in we had had both feet in the boat marked "self." The only safe place to be is to have both feet firmly planted in the boat marked Christ.
Or to change the picture, suppose that you were trying to cross from one cliff to another one which is a hundred feet away. It is five thousand feet down to the rocks below. You have, however, a one inch thick piece of rope which is capable of holding up several tons. There is a difficulty though, for you have only fifty feet of rope. I say, "Do not worry! I have fifty feet of thread. We can tie my thread to your rope and then tie that to trees on either cliff and then you can go across." You decline my offer and I respond, "What is the matter? Do you not trust the rope?" "Yes," you say, "I trust the rope but I do not trust the thread." Then let's change the story and make it ninety feet of rope and only ten feet of thread. You're still not comfortable. Then suppose we make it ninety-nine feet of rope and only one foot of thread. One inch of thread? You see, if you have one inch of thread, you will be just as dead on the rocks below as if you tried to cross on a hundred feet of thread. The rope obviously represents what Christ has done and the thread represents what we have done. We must trust in Christ alone. As Charles Spurgeon put it, "If we have to put one stitch into the garment of our salvation, we shall ruin the whole thing."