I realize many evangelicals do not like the term “religion” and even use it primarily in a negative way. However, we have to remember that the word is found in Scripture (e.g. James 1:26). Granted, we do have to define it properly, but we shouldn’t by default think of “religion” as a bad thing. For example, John Calvin called his now famous work the Institutes of the Christian Religion. In his work on the history of Reformed doctrine, Richard Muller spends some time discussing “religion” and its use/definition among Reformers and Reformed scholastics. Here’s his section on Calvin and the term “religion”:
This systematic approach to religion as the pattern of knowledge and worship directly related to faith and foundational to the elaboration of theology is profoundly evident in the successive editions of Calvin’s Institutes. In 1536 Calvin identified his work as an “institute” or instruction “of the Christian religion embracing almost the whole sum of piety and whatever it is necessary to know in the doctrine of salvation.” What is more, Calvin’s expansion of the Institutes, in which five chapters on the knowledge of God were added or developed as a kind of prologue, only serves to underscore in those introductory sections the primary emphasis on religion, piety and instruction in them.
Calvin’s 1539 expansion of this portion of the Institutes has a series of significant antecedents, not the least of which is Zwingli’s linking of the discussion of religion to the problem of the “knowledge of God” and the “knowledge of man.” Like Zwingli, moreover, Calvin rests much of his discussion on Cicero’s De Natura Deorum. Given the universal recognition, implanted in all human beings, that there is a God, Calvin argues, it would be sheer folly to claim that religion is a human invention: it is certainly true that wicked and “clever” persons have invented many superstitions designed to keep human beings in subjection, but it is equally clear that they would never have been able to do so had there not been a fundamental conviction of the existence of God and the need to worship him already present in all human beings. Given, moreover, the depth of human sinfulness and the extent of idolatry and superstition wrought by sin, Scripture is needed for the establishment of a right knowledge of God—and, by extension, for the establishment of true religion.
Although Calvin does not spell out the etymology and definition of “religion” in the detail one finds in Zwingli, the conception is quite similar: true religion must ultimately be grounded in the word of God and it is set apart from the false religions of idolatry and superstition. Nowhere is it assumed, moreover, that “religion” indicates a human phenomenon: even in its false forms, it presumes the fundamental sensus divinitatis and is grounded in the objective reality of the God who must be worshiped. This sensibility will carry over into Reformed orthodoxy.
(This quote is found on page 167 of PRRD, Volume 1)