The Apostle Paul wrote in Romans 12.11: Do not be slothful in zeal, be fervent in spirit. 

What does it mean to be “fervent in spirit”? Vance Havner once defined it in a sermon…

To be “fervent in spirit” is to be “boiling in spirit,” and to boil we must be near the Fire. How shall we obtain the burning heart? Jeremiah said it was God’s Word that did it and it was Jesus expounding the Scriptures that did it and it was while listening to Luther’s exposition of Romans that Wesley’s heart was warmed (Vance Havner, Hearts Afire, MCMLII, 12).

There you go! The key to possessing a fervent spirit is the reading, listening, studying and meditation on God’s Word.

Are we fervent in spirit?