וַיַּ֖עַשׂ אֶת־הַבְּרִ֣יחַ הַתִּיכֹ֑ן לִבְרֹ֙חַ֙ בְּת֣וֹךְ הַקְּרָשִׁ֔ים מִן־הַקָּצֶ֖ה אֶל־הַקָּצֶֽה׃
And he made the middle bar to pass through in the midst of the boards from the one end to the other.
Read kabbalistic (mystical) interpretation of Exodus 36:33: and classical mystical sources.