"If you were God's children you would loathe the very thought of the world's evil joys, and your question would not be, 'How far may we be like the world?' but your one cry would be, 'How far can we get away from the world? How much can we come out from it?'" Your temptation would be rather to become sternly severe, and ultra-Puritanical in your separation from sin, in such a time as this, than to ask, 'How can I make myself like other men, and act as they do?' Brethren, the use of the church in the world is that it should be like salt in the midst of putrefaction; but if the salt has lost its savor, what is the good of it? If it were possible for salt itself to putrefy, it could but be an increase and a heightening of the general putridity. The worst day the world ever saw was when the sons of God were joined with the daughters of men. Then came the flood; for the only barrier against a flood of vengeance on this world is the separation of the saint from the sinner. Your duty as a Christian is to stand fast in your own place and stand out for God, hating even the garment spotted by the flesh, resolving like one of old that, let others do as they will, as for you and your house, you will serve the Lord." (Source: How to Become Fishers of Men)
Recommended reading:
You can also listen to an audio recording of The Forgotten Spurgeon on Sermonaudio.com: