Rabbi Yossi raised a fundamental question about the boundary between heaven and earth. He cited (Psalms 115:16), which declares that "the heavens are the heavens of the Lord, and the earth He gave to humankind." If heaven belongs exclusively to God and earth to humanity, how could any mortal ever cross that boundary?
The answer, according to Rabbi Yossi, is that no one actually did. Moses did not ascend into heaven, and Elijah did not ascend above the heavenly realm. The divine glory, for its part, did not descend to earth. The boundary between the two domains remained intact.
What happened at Sinai, then, was something more subtle and extraordinary. God called to Moses from the top of the mountain, and Moses climbed up to meet Him there. The mountaintop became a kind of threshold, a meeting point between heaven and earth that belonged fully to neither. As the Torah records in (Exodus 19:20), "The Lord called Moses to the top of the mountain, and Moses ascended."
This teaching preserved in the Mekhilta DeRabbi Yishmael pushes back against the idea that Moses literally entered heaven. The mountain's summit was as high as any human could go. God lowered His presence to the peak, and Moses raised himself to the peak, and the two met at the boundary. The cosmic order held. Heaven remained heaven, earth remained earth, and the Torah was given at the seam between them.