Another interpretation: Because the Holy One, blessed be He, appeared to them at the sea as a warrior waging war, and appeared to them at Sinai as a scribe teaching Torah, appeared to them in the days of Solomon as a young man, and appeared to them in the days of Daniel as an elder, the Holy One, blessed be He, said to them: It is not because they see Him in many forms [that there is more than one God]. I am He who was at the sea; I am He who was at Sinai. "I am the LORD your God."
Why God Appears as Warrior, Scribe, Youth, and Elder
Midrash Tanchuma Buber, Yitro 16:2
ד"א לפי שנראה להם הקב"ה בים כגבור עושה מלחמה, ונראה להם בסיני כסופר מלמד תורה, נראה להם בימי שלמה כבחור, ונראה להם בימי דניאל כזקן, אמר להם הקב"ה לא בשביל שהם רואים אותו דמויות הרבה, אני הוא שבים, אני הוא שבסיני, אנכי ה' אלהיך.