"And the fruit of righteousness are sown in peace by those who make peace."
Note, non-count usage here (old usage probably), but fruit refers to one thing, not more; i.e., 'the reward (which richeousness brings)":
For the seed which one day produces the reward which righteousness brings can only be sown when personal relationships are right and by those whose conduct produces such relationships. (James 3:18; William Barclay's Daily Bible Study) In this verse, James is talking about a social situation. God's purpose—the fruit that He wants from His way of life, the kind of character that He wants in us—has to be produced in peace. It cannot be produced in war.
 "The fruits of righteousness have to be sown!That is work.
Note, count here: fruits refers to love, joy, peace, gentleness, goodness, meekness, kindness, faith, self-control—
We see a process. As those fruits
begin to be produced, ... "
Note, again count here: fruits refers back to love, joy, peace, and so on.
 ... sanctification cannot be hidden any more than the fruit
on a tree can be hidden.
Note, non-count usage here: common modern day usage.
 We will never attain to holiness without Bible study, prayer, fasting, meditation, and obedience because through them is how spiritual life is sown, cultivated, fertilized, and tended so that fruit
Note, count usage again: fruit refers to "the reward which richeousness brings."