וַֽיהוָ֞ה הֶאֱמִֽירְךָ֣ הַיּ֗וֹם לִהְי֥וֹת לוֹ֙ לְעַ֣ם סְגֻלָּ֔ה כַּאֲשֶׁ֖ר דִּבֶּר־לָ֑ךְ וְלִשְׁמֹ֖ר כָּל־מִצְוֺתָֽיו׃
And the LORD hath avouched thee this day to be His own treasure, as He hath promised thee, and that thou shouldest keep all His commandments;
Read kabbalistic (mystical) interpretation of Deuteronomy 26:18: and classical mystical sources.