Exodus 26:15

ועשית את הקרשים AND THOU SHALT MAKE THE BOARDS — It should be said: “Thou shalt make boards” (without the definite article), the same form which is used of each of the other things (parts of the Tabernacle)! What is the force of the term, “the boards?” It speaks of those boards that already existed as being designated for that purpose. For our father Jacob had planted cedars (shittim-trees) in Egypt and when he died be bade his sons carry them up with them when they would leave Egypt. He told them that God would once command them to erect a dwelling of shittim-trees in the wilderness. “See” — added he — “that they be ready in your possession!” (cf. Rashi on Exodus 25:5). That is what the Babylonian embodied in his liturgical composition: The plant of those who had been admonished by their father Jacob grew up rapidly to become the cedars for the beams of our House (the Tabernacle), which refers to the fact that they had been admonished that they (the cedars) should be ready in their possession in advance (before they were needed). עצי שטים עמדים OF SHITTIM-WOOD STANDING UP — Estantivs in old French; Engl, perpendicular. — This means that the length of the boards shall be placed perpendicular in the walls of the Tabernacle and that you shall not make the walls of the boards placed horizontally so that the breadth of the boards should be along the height of the walls, one board upon the other.

וְעָשִׂ֥יתָ אֶת־הַקְּרָשִׁ֖ים לַמִּשְׁכָּ֑ן עֲצֵ֥י שִׁטִּ֖ים עֹמְדִֽים׃

And thou shalt make boards for the tabernacle of shittim wood standing up.