Martin Luther wrote, in connection with Rom 12:11’s τῷ πνεύματι ζέοντες-
Be fervent in spirit. Those who snore and yawn and are lukewarm in all their efforts are the people who break this command, and they achieve nothing by their works but only dissipate them, Prov. 18:9: “He who is slack in his work is a brother to him who destroys.” But people of this kind are also hateful to men, to say nothing of God. Thus it is that today very commonly the artisans who have been hired do their work as if they were asleep. And the religious and the priests literally snore during their prayers, even physically, to say nothing about the sleepiness of their minds, and they do everything with the greatest laziness. Here the apostle therefore is speaking against this deadly sin of acedia, or being tired of doing good works. The Greek word ἀκηδία means “tedium,” or “boredom,” or “indifference.”
This sin is so widespread that hardly anyone deigns to be attentive. And because people are unwilling to serve with a fervent spirit, it is necessary that they become fervent in the flesh. For they must be fervent in one of the two, either the spirit or the flesh. And the fervor for one is the freezing out or extinction of the other, except where by God’s permission in time of temptation the spirit still is aglow even in the midst of the fervor of the flesh.
Therefore the man who does his work with lukewarmness of necessity will be fervent in the flesh. And on that account he is compelled as it were to “waste the work” which he performs, because of the fervor of the flesh. So a lazy cook, about to prepare a meal, does his work in such a way that the food gets cold during the serving. Who would not despise him, and rightly?
Truly said, Martin. Truly said.