שִׁ֥יר הַֽמַּֽעֲל֗וֹת לִשְׁלֹ֫מֹ֥ה אִם־יְהוָ֤ה ׀ לֹא־יִבְנֶ֬ה בַ֗יִת שָׁ֤וְא ׀ עָמְל֣וּ בוֹנָ֣יו בּ֑וֹ אִם־יְהוָ֥ה לֹֽא־יִשְׁמָר־עִ֝֗יר שָׁ֤וְא ׀ שָׁקַ֬ד שׁוֹמֵֽר׃
A Song of Ascents; of Solomon. Except the LORD build the house, They labour in vain that build it; Except the LORD keep the city, The watchman waketh but in vain.
Read kabbalistic (mystical) interpretation of Psalms 127:1: and classical mystical sources.