The burning bush
Moses was an Egyptian prince. As a prince he had everything done for him; he was the famous son of an Egyptian princess. As a shepherd he had to do everything for himself. He was holding the very job he had been taught to despise (Genesis 43:32; 46:32-34). What a humbling experience this must had been for Moses. But God was preparing Moses for leadership. Living the life of a shepherd and nomad. Moses couldn't see this himself.
God spoke to Moses from an unexpected source: a burning bush. God often uses unexpected sources when working in our lives too, whether people, thoughts, or experiences. Be willing to investigate, and be open to God's surprises.
Moses saw a burning bush and spoke with God. When the slaves were freed from Egypt, God led them by a pillar of cloud and fire. God made such appearances to encourage his new nation, to guide them, and to prove the reliability of his verbal message.
At God's command, Moses removed his shoes and covered his face as well. God is our friend, but he is also our sovereign Lord. If necessary, adjust your attitude so it is suitable for approaching a holy God.
Reference summary used from Life Application Bible, KJV, Tyndale House Publishers, Inc., Wheaton, IL