The following is from John Newton's letters.
Conformity to the world is the bane of many professors in this day. They have found a way, as they think, to serve both God and Mammon. They may attain to a scheme of orthodox notions--but they will remain destitute of the life, power, and comfort of piety--so long as they cleave to those things which are incompatible with it.
We must not conform to the spirit of the world. As believers, we are strangers and pilgrims upon earth. Heaven is our country, and the Lord is our King. We are to be known and noticed as His subjects; and therefore it is His desire, that we do not adopt the sinful customs of the land in which we sojourn.
We must not conform to the maxims of the world. The world in various instances calls evil good, and good evil. But we are to judge of things by the unerring Word of God--uninfluenced by the determination of the great, or the many.
We must not conform to the world in their amusements and diversions. "What fellowship has light with darkness, or what concord has Christ with Belial?" What does a believer have to do into those places and companies, where everything tends to promote a spirit of dissipation; where the fear of God has no place; where things are purposely disposed to inflame or indulge corrupt and sinful appetites and passions, and to banish all serious thoughts of God and ourselves?
If it is our duty to redeem time, to walk with God, to do all things in the name of our Lord Jesus Christ, and to follow the example which He set us when he was upon earth. It must of course be our duty to avoid a conformity with the world in those vain and sensual amusements, which stand in as direct contradiction to a spiritual frame of mind. So far as a Christian is infected by a conformity to the spirit, maxims, and sinful customs of the world, true piety will be hindered.
May the Lord enable you and I to lay this subject to heart, and that we be preserved from that growing evil--a sinful conformity to the world!