not lagging in diligence; fervent in spirit; serving the Lord;

But the day of the Lord will come as a thief in the night; in which the heavens will pass away with a great noise, and the elements will be dissolved with fervent heat, and the earth and the works that are in it will be burned up.

looking for and earnestly desiring the coming of the day of God, which will cause the burning heavens to be dissolved, and the elements will melt with fervent heat?

Like silver dross on an earthen vessel are the lips of a fervent one with an evil heart.

This man had been instructed in the way of the Lord; and being fervent in spirit, he spoke and taught accurately the things concerning Jesus, although he knew only the baptism of John.