Exodus 10:9--And Moses said, We will go with our young and with our old, with our sons and with our daughters, with our flocks and with our herds will we go; for we must hold a feast unto the LORD.
Repetition is a commonly used literary tool, especially in lists, probably because it is so effective and easily used. It's almost natural. By using it, writers or orators can add emphasis to certain points or draw contrast between them. Here, Moses uses it to encompass the entire nation of Israel in every aspect.
Moses and Aaron have gone before Pharaoh once again, requesting permission to leave Egypt, go three days into the wilderness, and worship God. The plague of hail has just occurred, and Moses and Aaron have warned Pharaoh about the plague of locusts. This time, Pharaoh said, "Go, serve the LORD your God: but who are they that shall go?" And Moses answered with the above verse: "We will go with our young and with our old, with our sons and with our daughters, with our flocks and with our herds...."
Moses' answer contains two points of repetition: 1) Repetition of the word "with" emphasizes the fact that every item listed will be included, and 2) repetition of a phrase containing two opposites. The first phrase is young and old, the second sons and daughters, and the third flocks and herds (sheep and cattle).
So what's the lesson? Well, by using repetition, Moses made sure Pharaoh knew that every person had a part and a job in worshiping the Lord. It should be the same way today. It is every person's job, every person's obligation, every person's privilege to serve and worship the Lord God almighty. It doesn't matter how old you are, what gender you are, what color or creed you are, where you live, how much money you have, or what talents you have, you have a place in praising and worshiping God. We are not worthy to serve Him or praise Him, but He is worthy of all praise, glory, honor, and thanks. The greatest thing is that God loves us and wants it from us. So let's give it to Him, shall we?
In the words of the Psalmist in Psalm 150, verse six: "Let everything that hath breath praise the LORD. Praise ye the LORD."