"Bear[ing] fruits worthy of repentance" implies a process. Just as a tree does not produce fruit overnight, a Christian does not fully repent overnight. It is a lifelong process of making changes, and over time we will produce the fruit of the Spirit more consistently than the works of the flesh.
Martin G. Collins
Basic Doctrines: Repentance
We have a choice in this process. If we choose correctly, the fruits of that Spirit—the results of making correct choices—will begin to give evidence of the Spirit in us.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part 9)
The context in which these verses appear is important to understanding the production of the fruit of the Spirit. This immediately precedes the listing of the fruit of the Spirit, showing that Paul means that they will be produced through much internal conflict.
This is true because obedience to God's Word is required to produce the Spirit's fruit, and the Christian is being pulled or led in two directions. The one tries to make us satisfy the desires of our old nature, and the other leads us toward producing the fruit of the new. Paul expresses his experience with this in Romans 7:15-19.
For what I am doing, I do not understand. For what I will to do, that I do not practice; but what I hate, that I do. If, then, I do what I will not to do, I agree with the law that it is good. But now, it is no longer I who do it, but sin that dwells in me. For I know that in me (that is, in my flesh) nothing good dwells; for to will is present with me, but how to perform what is good I do not find. For the good that I will to do, I do not do; but the evil I will not to do, that I practice.
Christians, as Martin Luther stated, "are not stocks and stones." As humans, we are creatures of desires, drives, and emotions. Certainly, as we learn to walk in the Spirit, we increasingly subdue our flesh. But flesh and Spirit remain, and the conflict between them is fierce and unremitting.
We need not become discouraged over this conflict, though, because Paul also gives us a very hopeful solution. In Romans 7:24-25, he exclaims: "O wretched man that I am! Who will deliver me from this body of death? I thank God—through Jesus Christ our Lord! So then, with the mind I myself serve the law of God, but with the flesh the law of sin."
Every Christian striving to produce the fruit of God will experience this combination of lamentation over sinfulness and joyous expression of gratitude over the certainty of deliverance. The unconverted do not feel the agonizing struggle against sin with the same intensity as the converted. The converted have their peace disturbed and can feel wretched in their conscience.
But this has a good side to it as well. We know it is degrading to the divine nature, and it humbles us to know full well that we have succumbed to evil passions. We then realize more fully that the law cannot come to our aid, neither can other men, and our strength has already betrayed us. Therefore, if we really desire to glorify God and produce spiritual fruit, this conflict will drive us to God in heartfelt prayer for the strength only He can give. God's Word and eventually our experience prove that without Christ, we can do nothing!
John W. Ritenbaugh
The Fruit of the Spirit