Albert Barnes Commentary Numbers 7:89

"And when Moses went into the tent of meeting to speak with him, then he heard the Voice speaking unto him from above the mercy-seat that was upon the ark of the testimony, from between the two cherubim: and he spake unto him." — Numbers 7:89 (ASV)

With him – that is, as the margin indicates, “with God,” not, as some interpret, with himself.

He heard the voice of one speaking – Rather, he heard the voice speaking, or conversing. The effect was as though Moses was audibly addressed by another person; how this effect was produced, we are not told.

Thus, the promise of Exodus 25:20-22 was fulfilled; this fulfillment was an immediate response from God to the cheerful readiness with which the tribes had made their offerings and supplied everything necessary for the Holy place and its service.

With all now complete as God had appointed and the camp purified from defilements, God meets Moses, the mediator of the people—not as before on the distant peak of Sinai, but in their midst, in the dwelling-place that He from then on graciously chose to inhabit.