James 4:4 - Matthew Poole's English Annotations on the Holy Bible

Ye adulterers and adulteresses; he means adulterers and adulteresses in a spiritual sense, i.e. worldly-minded Christians, who being, by profession, married to the Lord, yet gave up those affections to the things of the world which were due to God only. The like expression is used, Matthew 2:39; Matthew 12:4. Know ye not; ye ought to know, and cannot but know. That the friendship of the world; inordinate affection to the world, addictedness or devotedness to the things or men of the world. Is enmity with God; alienates the sole from God, and God from it, 1 John 2:15. Whosoever therefore will be a friend of the world; if it be the purpose and resolution of a man's heart to get in with the world, though perhaps he cannot obtain its favour; he courts it, though it be coy to him. Is the enemy of God; exerciseth hostility against God, by adhering to an interest so contrary to him.