Cut a rectangular piece of leather about 2 inches bigger than your Book of Mormon on all sides. You can measure your Book of Mormon with a ruler or place it on the leather to estimate the size.
Measure a second piece of leather to match the length (long side) of the first. Cut this piece to be identical in length but twice as wide as the first piece.
Line up both pieces of leather so that they match on three edges. Place the leather pieces face to face, so that you can see the back of each piece.
Sew three edges of the leather together with a sewing machine. Leave a margin of 1/2 inch to 1 inch. Stop sewing two of the edges when you reach the end of the smaller piece. The remaining portion of the larger piece of leather will serve as the flap to close the pouch.
Turn the pouch inside out. This will hide the stitching and create an even seam. Use a pen or pencil to push the corners of the pouch all the way out.
Punch a hole near the top edge of the larger pieces of leather. Thread leather cords through the hole and secure them with a knot. Place the Book of Mormon inside the pouch and fold the flap over the front. Wrap the loose ends of the leather cords around the pouch to hold it closed.