We're not about religion, man
Why have so many Christians equated "religion" with "legalism?" Take a look at this:
This dude makes some good points, no doubt. But everything he says about religion seems to be aimed properly at legalism.
Some thoughts here.
1. The English word religion is used to describe belief and practice with reference to supernatural things. For Christians, this encompasses belief in the revelation of God, and obedience to the forms of worship proscribed thereby. Thus our religion is found in the Scriptures. Jesus Christ, as the great prophet of God, gave us forms of worship to submit ourselves to. These include the means of grace--baptism, the Lord's supper, the preaching of the Word--but also certain aspects of worship such as the observance of a day of rest, meeting together in a group, forms of prayer, etc.
2. From this we can see why older writers employed the word religion quite freely (and properly) to describe Christian worship and practice.
3. The entire Bible, old and new, along with godly expositors of it in every generation, have carefully distinguished between godly religious practice("worshiping in Spirit and truth," per John iv), which is internal and external according to the Word, and false or hypocritical worship, which is either invented, or merely external.
4. These are the two evils: an invented religion of man, or else a bare external observance. Because all religious practice is aimed at a unified communion with God (relationship, we would say, though we should more carefully define what we mean by that), it needs to be done both according to his command, and with the whole self. To alter either of those overthrows the whole purpose of religion. Or more precisely, makes true religion false.
5. In both of those we can see Keller's two thieves (an apt metaphor) of legalism and antinomianism. The Pharisees of the new testament emptied true religious observance of meaning (ex. praying in the streets to be seen), and invented complex religious practice designed to bring about communion with God. This is legalism. Paul fought both of these when men tried to alter the conditions of men's approach to God to include various legal observances.
6. So certainly, false religion always includes in it legalism. Also, the prescribed forms of religion for the church, such as prayer, fellowship, Lord's supper, when made merely external, are legalistic.
7. But why conflate the two? Probably because many Christians are embarrassed about various abuses which have flown under the banner of Christianity, such as the Crusades and the Inquisition. Also, perhaps they attempt to remove the objection they hear before it can even be made. "I'm just not into religion." "Ah, but neither was Jesus!" they say. Boom, objection answered, though of course what lay behind the objection was a rejection not of religion but of God.
8. Who cares though? Words are constantly changing their meaning. If you read "cleave" in a seventeenth century book it means to cling to something. But the most common usage nowadays is to split something apart. That's nothing to get mad about, it is just the common evolution of language. It annoys me as all poorly defined cliches do, but many things annoy me without needing a long blog post (a short facebook status suffices for most).
9. In this case, it matters because there is a communication disconnect between audience and the speaker. The definition of religion held in mind by the speaker is not the same as the one held in mind by the listener. When a non-Christian says "religion," they do not necessarily mean legalism. Even many Christians do not mean "legalism" when they say "religion." Communication is important, and since English translations of the Bible do not include this legalism-religion equivalency, we are holding our audience captive to a position they cannot find for themselves in the Scriptures.
10. We therefore do them a disservice by not speaking the Biblical language to them, and by denying that religion is what we offer, we deal in bad faith with them. For the Christian MUST be participative in the forms of religion that Jesus has given! Religion is no enemy, except when legalistic.