Then He said, “Hear now My words: If there is a prophet among you, I, the LORD, make Myself known to him in a vision; I speak to him in a dream. Not so with My servant Moses; He is faithful in all My house. I speak with him face to face, Even plainly, and not in dark sayings; And he sees the form of the LORD. Why then were you not afraid To speak against My servant Moses?”— Numbers 12:6-8 NKJV
Moses had a very unique relationship with G-d. G-d lifted up Moses and defended him and stated that Moses was faithful in all G-d’s house. This meant that there was no one more faithful than Moses at this time.
Moses’ relationship was so unique that G-d stated that He spoke with Moses plainly, without dark mysterious sayings. G-d also pointed out that Moses sees the form of the L-RD.
He then asks Aaron and Miriam, “Why then were you not afraid to speak against My servant Moses?”