Crystal and Jerry, today you join your separate lives together. The two separate bottles of sand symbolize your separate lives, separate families and separate sets of friends. They represent all that you are and all that you will ever be as an individual. They also represent your lives before today.
As these two containers of sand are poured into the third container, the individual containers of sand will no longer exist, but will be joined together as one. Just as these grains of sand can never be separated and poured again into the individual containers, so will your marriage be.