Luther on John 15:5

I am the vine; you are the branches. Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing.

Note that this is what He means when He says: “He that abideth in Me, and I in him, the same bringeth forth much fruit.” He wishes to point out that Christianity is not attached to the outside of a man or put on as a garment, that it is not the adoption of a new method and manner of life and action, like monasticism and self-chosen sanctity, but that it is a new birth through God’s Word and Spirit and the creating of a man who is entirely new from the bottom of his heart. But thereafter, once the heart is born anew in Christ, fruits also flow: the confession of the Gospel, works of love, obedience, patience, chastity, etc.
So Christ would herewith forewarn His disciples to be sure to stay with His Word, which makes real Christians, people with a new life and nature, who bring forth may fruits from the Vine, and to beware of all kinds of other teaching, which inverts the order and wants to make the tree out of the fruit and grapes out of thorns and thistles. For nothing will ever come of this attempt. - Luther

This idea, the idea of outward works still threaten us today, even though we don't have monasteries and the like. What we have is the outward appearance of being "good" -- the monks were the "good" Christians of their day, and we today have our own self-created ideas of what a "good" Christian looks like. And we are tempted to put that image of the "good" Christian on us, to keep up appearances, to have people applaud us because of our actions.

That's not the way it works. That is doing nothing. Repent. Hear the Gospel. And Christ will give you His life, and you will show forth love, not ape your pious appearing neighbor.