John Wesley on Exodus 17:15

And Moses built an altar, and called it Jehovah - niffi - The Lord is my banner. The presence and power of Jehovah was the banner under which they were lifted, by which they were animated, and kept together, and therefore which they erected in the day of their triumph. In the name of our God we must always lift up our banners: He that doth all the work should have all the praise. Write this for a memorial - This is the first mention of writing we find in scripture; and perhaps the command was not given till after the writing of the law on tables of stone.