He wanted to caution them that the luxury of prosperity could make it easy to forget how dependent they were on the Lord at all times. They needed to realize that without the strength God provided they couldn't even raise their food to their mouths. Moses' instruction also applies to us. We must keep remembering what God has done for us, praising Him for what He has given us, and thanking Him for His forgiveness. Always remember to forget The troubles that pass your way, But never forget to remember The blessings that come each day.
Memory is the wellspring of praise.