On the 1st of Sivan, 2448, the Children of Israel arrived at Mount Sinai in the Sinai Desert and camped at the foot of the mountain “as one man, with one heart” in preparation for the receiving of the Torah from G-d:
“In the third month of the children of Israel’s departure from Egypt, on this day they arrived in the desert of Sinai. They journeyed from Rephidim and came to the Sinai desert, and camped in the desert; and Israel camped there, before the mountain”. (Shemot, 19:1)
In his commentary on these verses, Rashi notes the grammatically unconventional use of the singular vayichan (“and he camped,” rather than vayachanu, “and they camped”) in speaking of the entire Jewish people. Rashi explains that the Torah wishes to inform us that “they camped as a single man, with a single heart, unlike all other encampments, which were accompanied by dissent and dispute.”
This was the essential preparation to the giving of the Torah.