Fervent, which is formed from the participle of the Latin ferveo, to boil or ferment, is an exact translation of this word, which means to seethe or bubble, and is therefore used figuratively of mental states and emotions. See on leaven, Mat 13:33.
Diligently (ἀκριβῶς)
Rather, accurately; so far as his knowledge went. The limitation is given by the words following: knowing only the baptism of John. See on Luk 1:3; and compare the kindred verb, inquired diligently, Mat 2:7, where Rev. renders learned carefully.