This image comes from the East and is usually associated with Chan (Zen) Buddhism and martial arts. The finger pointing at the moon analogy was used by the master to teach their students to look beyond simple techniques.
The finger pointing is the scripture or the teacher or an image and is the vehicle for understanding something, for instance, God but the finger is not the moon or God. The moon represents the object the finger points to, reality or truth.
To often we Catholics get all rapt up in the outer trappings of our faith and forget what our true focus should be, namely God. Saying devotion like the rosary or Divine Mercy, having images of Mary, Christ or one of the saints, reciting the divine office or a memorized prayer are all good practices that can deepen our faith life but they are not the end all to knowing God. They point to God.
What is important is looking beyond the outer trappings of our faith and seeing the Glory of God and the Mystery of Christ in us and all around us. We may not be able to put things into words but we know because we know in our hearts.
We must always turn inward, to the heart to encounter Christ. If devotions or prayers help us do this, all is fine and good as long as we remember they are only a pointer pointing to Christ. We can do this without these pointers by just sitting still and turning our gaze inward to the heart.
Excerpt from A FINGER POINTING TO THE MOON: Considerations on Living as a Lay Monk By John Waligorski
A Finger Pointing to the Moon 