Jamieson, Fausset and Brown on James 3:14

14. if ye have--as is the case (this is implied in the Greek indicative).

bitter--Ep 4:31, "bitterness."

envying--rather, "emulation," or literally, "zeal": kindly, generous emulation, or zeal, is not condemned, but that which is "bitter" [Bengel].

strife--rather, "rivalry."

in your hearts--from which flow your words and deeds, as from a fountain.

glory not, and lie not against the truth--To boast of your wisdom is virtually a lying against the truth (the gospel), while your lives belie your glorying. Jas 3:15; Jas 1:18, "The word of truth." Ro 2:17, 23, speaks similarly of the same contentious Jewish Christians.