The Midrash Mechilta, on the first of the Ten Commandments asks why G-d identifies Himself as the One who took us out of Egypt, instead of the Creator of the Universe?

The Mechlita answers that G-d appeared to the Jewish People as a Youthful Warrior at the Red Sea, but at Mount Sinai He appeared as an Elderly Scholar. Thus, G-d assured us that He was One and the Same on both occasions, despite different appearances.

However, the Rambam in his Thirteen Principals of Jewish Faith states that G-d has no physical features. How could He appear as a man on both occasions? The Rambam can not contradict the Midrash Mechlita.

The answer is that the Jewish People's conception and our Relationship to Him differed and needed to see Him as human on these two occasions. Just a week before the splitting of the Red Sea, the Jewish People were slaves in Egypt. G-d freed the Jewish People and enabled us to escape from the pursuing Egyptians and into the Red Sea. G-d cast the drowned Egyptians and their Jewelry on the shore at the feet of the Jewish People, who reacted by proclaiming Him as the Eternal King. They then sang the Song of the Red Sea in gratitude for His great miracles.

Six weeks later, at Mount Sinai, we witnessed and were awed by G-d's decent from Heaven. G-d was escorted by millions of Angels, and His Presence caused Mount Sinai to explode in fire and smoke. There were Spectacular sounds and sights climaxed by G-d's Voice as He gave us the Torah.

Once again, as at the Red Sea, we proclaimed G-d as the Eternal King. Now it was not based solely on our gratitude for freeing us from bondage as our personal redeemer, it was based on G-d being the Creator of the entire universe.

At the Red Sea, our conception of G-d was influenced by our appreciation and gratitude for saving us from the Egyptians. Thus we saw him as a Youthful Warrior in a human form. When we stood at Mount Sinai to receive the Torah, our conception of G-d had matured to that of a Human Elderly Scholar.

G-d has absolutely no physical features, but our perception of Him changes as we progress and grow spiritually. Thus, Rambam and the Mechilta are consistent.