עַל־פִּ֣י יְהוָ֗ה יִסְעוּ֙ בְּנֵ֣י יִשְׂרָאֵ֔ל וְעַל־פִּ֥י יְהוָ֖ה יַחֲנ֑וּ כָּל־יְמֵ֗י אֲשֶׁ֨ר יִשְׁכֹּ֧ן הֶעָנָ֛ן עַל־הַמִּשְׁכָּ֖ן יַחֲנֽוּ׃
At the commandment of the LORD the children of Israel journeyed, and at the commandment of the LORD they encamped: as long as the cloud abode upon the tabernacle they remained encamped.
Read Kabbalistic (mystical) interpretations of Numbers 9:18: Zohar and classical Jewish mystical sources, free online.