Every branch that does bear fruit He prunes, that it may bear more fruit. John 15:2
An able vinedresser is not content with a good vine and true branches; he would like to have vines and branches that bear much fruit. Therefore he hastens to work on them, to trim and prune them, and to remove the superfluous leaves; he aids and tends them to improve their growth and fertility. This results if the vine is cultivated and watched over in such a way. God does the same thing with every Christian on His vine, whether he is preacher, pupil, or hearer. He does not let him be idle but sends him trials which compel him to exercise his faith; He lets the devil and the world hound him with external and internal persecutions. Thereby He purifies and trims the branches, to make them stronger and better. All this is done that they may bear all the more fruit; that their faith may assert itself more and more and, by reason of trials, may become sure and strong; that they may praise God all the more, pray, preach, and confess. Then the Word and its power will increase everywhere. This applies both to the believers, who themselves become stronger in faith and in knowledge, and to many others, who are to be brought to faith by them. The result will be fruit that is not only large and perfect but, as Christ says here, also abundant. (Luther’s Works 24: Sermons on the Gospel of St. John Chapter 14-16; Concordia Publishing House; 200)