As far as the assurance of the believer of eternal life is concerned, that to my mind is the best way to talk about security. It's the doctrine of eternal life. Mr. Spurgeon was right when he said, "I believe not so much in the perseverance of the saints as in the perseverance of the Savior." And so we believe that, because the Lord Jesus perseveres in securing and maintaining in a saved condition the saints for whom he died, we can be confident that if we have truly believed in him and possess eternal life, we shall one day be in his presence. Some men still object to the doctrine of the perseverance of the saints, but if true saints, by their confession, will persevere then it's equally true that the saints must persevere. So we can say the saints must persevere because they will persevere. So we are confident that having believed in the Lord Jesus Christ, we shall persevere because he perseveres. And these "ifs" are tests for professors and they also remind us that we need to constantly look at our own lives and see if it's really true that we do have eternal life. - S. Lewis Johnson in a sermon on Colossians 1:21-23.