Sri Chinmoy: “Aum” is God in His three aspects: God the Creator, God the Preserver and God the Destroyer. But “Destroyer” is the wrong term. God is not the Destroyer but the Transformer. Anything that is undivine in us God transforms and illumines. “A” represents God the Creator, “U” represents God the Preserver and “M” represents God the Transformer.
God the Creator has created us. God the Preserver preserves us. But while preserving us He notices some imperfection in us and He tries to perfect us. When He is perfecting us, He becomes God the Transformer. So when we chant “Aum”, we invoke God in His three aspects.