I think Christ put it pretty clear in Jn 14:15 as you quoted. But, what I have come to understand in it's full meaning is to keep the Word of God in your heart and on your mind, by seeking first the kingdom [Matt 6:33]. If we center our lives upon Christ, and the Word which is Christ, then we obey and keep His commandments, which are to love God with all our heart, mind, soul, and to love our neighbor. By thinking first of Christ (What Would Jesus Do) [WWJD], then each thought and action is directed by the Spirit, and therefore living in obedience to the will of God. This is how the body of Christ shares it's light with the world. This is the love of Christ in us working through us. This is how we become His hands, His feet, His eyes. This is the power of the cross through His people.