וְחַ֤ג שָׁבֻעֹת֙ תַּעֲשֶׂ֣ה לְךָ֔ בִּכּוּרֵ֖י קְצִ֣יר חִטִּ֑ים וְחַג֙ הָֽאָסִ֔יף תְּקוּפַ֖ת הַשָּׁנָֽה׃
And thou shalt observe the feast of weeks, even of the first-fruits of wheat harvest, and the feast of ingathering at the turn of the year.
Read kabbalistic (mystical) interpretation of Exodus 34:22: and classical mystical sources.