Galatians 5:22-23 (NKJV)
But the fruit of the Spirit is love, joy, peace, longsuffering, kindness, goodness, faithfulness, gentleness, self-control. Against such there is no law.
Notice how this verse does not speak of the fruits (plural) but only of the fruit (singular). Yet, it goes on to list all the fruits. This gives double emphasis on the first fruit in the list which is love. Out of this one fruit, love, come the others. Jesus warned about false prophets and said "You will know them by their fruits." Bad trees do not bear good fruit and good trees do not bear bad fruit. So if you want to know if someone is filled with the Holy Spirit, just look for this list of fruit.
This list of virtues is in opposition to a list of vices given in an earlier verse. That previous list was called the "works of the flesh" and is contrasted to this list of the "fruit of the Spirit." There is something interesting to be learned by the difference between works and fruit. In John, chapter 15, Jesus speaks of himself as the vine and of us as the branches. He wants us to bear much fruit. How does a branch bear fruit? Does it have to strain to do so? No, all the branch does is to bear it; there is not work there. You can't force love, joy, peace. They only come from abiding in the Vine.