וְאִם־בְּאַחַ֖ת יִתְקָ֑עוּ וְנוֹעֲד֤וּ אֵלֶ֙יךָ֙ הַנְּשִׂיאִ֔ים רָאשֵׁ֖י אַלְפֵ֥י יִשְׂרָאֵֽל׃
And if they blow but with one, then the princes, the heads of the thousands of Israel, shall gather themselves unto thee.
Read kabbalistic (mystical) interpretation of Numbers 10:4: and classical mystical sources.