“For if these things are yours and abound, you will be neither barren nor unfruitful in the knowledge of our Lord Jesus Christ.”
“Unfruitful” is a metaphor that comes from trees and fields. Metaphorically, “unfruitful” means works or deeds that produce no fruit (Mt 13:22; Mk 4:19; 1 Co 14:14; Ep 5:11; Ti 3:14; Ju 12).
Figuratively, “unfruitful” means useless, unproductive.
Ep 5: 11 “And have no fellowship with the unfruitful works of darkness, but rather expose them.”
“Unfruitful” pertains to being useless in the sense of being unproductive. This person has no harvest, no fruit.
Ju 12 “… serving only themselves. They are clouds without water, carried about by the winds; late autumn trees without fruit, twice dead, pulled up by the roots.”
We need to recognize the moment of the harvest and seize its opportunity.
Some of us do not seize the season. At the time the fruit is ripe and the harvest is ready, we sleep. People in need of Christ walk in our presence and we do not recognize that need in them. Spiritually minded people are in tune to that need. As Jude says, we are so busy “serving only” ourselves that we cannot see the need of sharing Christ with someone else.