Dictionary of Biblical Words:
We get three religions spoken of in Scripture; the Jew’s religion (Gal. 1:13,14; Acts 26:5 synonymous in Paul’s time, alas, with formality and hypocrisy; vain religion, consisting in a mere profession with an unbridled tongue; and pare religion, which consists in visiting the fatherless and widows in their affliction, and keeping oneself unspotted from the world. We fear that the first two of these religions are still common, while the last is exceedingly rare, especially in the latter of its two qualities.
Concise Bible Dictionary:
This is applied in scripture to
1. The Jews’ religion, in which Paul was very strict (Acts 26:5).
2. Practical Christianity (James 1:26-27).
3. The character of the proselytes as “religious” or “worshipping” (Acts 13:43).