Christians who connect themselves with worldly associations are injuring themselves as well as misleading others. Those who fear God cannot choose the ungodly for companions, and be themselves unharmed… They are brought under the influence of worldly principles and customs, and through the power of association and habit the mind becomes more and more conformed to the worldling’s standard. Their love for God grows cold, and they have no desire for communion with Him. They become spiritually blind. They can see no particular difference between the transgressor of God’s law and those who fear God and keep His commandments. They call evil good, and good evil. The brightness of eternal realities fades away. The truth may be presented to them in ever so forcible a manner, but they do not hunger for the bread of life, or thirst for the waters of salvation. They are drinking at broken cisterns that can hold no water. Oh, it is an easy thing, by association with the world, to catch their spirit, to be molded by their views of things, so that we do not discern the preciousness of Jesus and the truth. And just to the degree that the spirit of the world dwells in our heart, it will control our life.
E. G. White, Selected Messages, bk. 2, pp. 128, 129