First, Miriam died. The same Miriam who had watched over Moses while he was floating in the Nile as a baby in a basket... the same Miriam who had led the women of faith in a triumphant song after the crossing of the Red Sea... that same Miriam, was gone.
Then, Aaron also died. In a very strange situation, God instructed Aaron and Moses to go up on Mt. Hor along with Eleazar, Aaron's son. There, God said, Aaron would die. And, he did. The position of high priest was passed on down to Eleazar on that day. So, only Moses remained. But, even Moses was on a downhill journey from this point forward.