וּבַחֲמִשָּׁ֨ה עָשָׂ֥ר יוֹם֙ לַחֹ֣דֶשׁ הַזֶּ֔ה חַ֥ג הַמַּצּ֖וֹת לַיהוָ֑ה שִׁבְעַ֥ת יָמִ֖ים מַצּ֥וֹת תֹּאכֵֽלוּ׃
And on the fifteenth day of the same month is the feast of unleavened bread unto the LORD; seven days ye shall eat unleavened bread.
Read kabbalistic (mystical) interpretation of Leviticus 23:6: and classical mystical sources.