Pick out a fabric pattern that would particularly appeal to the teenage girl you want to make the Bible cover for. Pick something that is fun to look at but also appropriate for church.
Measure the dimensions of the front cover and the spine of the Bible. For example, the cover might be 8 inches by 10 inches, and the spine 2 inches by 10 inches.
Add the width of the spine to the width of the front and back covers to get the width of the fabric you need to cut out for the fabric Bible cover. Add 0.5 inch to each measurement so you have room to sew.
For example, 8+8+2 = 18 inches wide, and 10 inches high; add 0.5 inch to get 18.5 inches wide and 10.5 inches high.
Subtract 1 inch from the width of the cover to get the size of the inner panels. These panels will be sewn to the larger piece of fabric to form the pockets that you will fit the Bible into. Add 0.5 inch to each measurement so you have room to sew. In the example, the pockets would be 8 - 1 = 7 inches wide, and 10 inches high. Add 0.5 inch to get 7.5 inches wide and 10.5 inches high.
Cut the cover and the two pockets out of your fabric.
Lay the larger piece of fabric face up on your sewing surface, and then the two smaller pocket pieces face down on the left and right sides of the larger piece of fabric.
Sew the pieces together, with the thread about 0.25 inch away from the edges of the fabric.
Turn the cover inside out and put it over your Bible.