Never be lacking in zeal, but keep your spiritual fervor, serving the Lord.
— Romans 12:11

"Keep your spiritual fervor" literally means "keep being boiling". A follower of Jesus should be "boiling" with enthusiasm in living for and serving Jesus, and pursuing those things He loves.

But not a self-created boiling. It must be conceived and driven by the Holy Spirit. This is a by-product of spending time in scripture and prayer and living a life of obedience.

Bottom line? God wants us to be PUMPED about serving Him, seeking the lost, and building the church.