standing upright

 Rashi comments (25:16):  יעקב אבינו נטע ארזים במצרים, וכשמת ציוה את בניו להעלותן עמהן כשיצאו ממצרים, שעתיד הקב״ה לצוות אתכם לעשות משכן במדבר מעצי שטים, ראו שיהו מזומנין בידכם.

Where did the wood to build the mishkan come from?  Yaakov planted cedar trees in Egypt and instructed his children that when they leave, they should take the wood with them, as it would be needed to build a mishkan.  

R' Baruch Mordechai Ezrachi asks: Just like Hashem made a miracle and the winds blew the precious stones needed for avnei shoham and avnei miluim into the camp of Bnei Yisrael, so too, Hashem could make a miracle and somehow Bnei Yisrael would find the wood needed for the mishkan.  Why did Yaakov go out of his way to plant trees?

There is a big difference between precious stones and wood for beams.  You can't make a diamond or a ruby or an emerald.  You can just discover them.  A tree, however, can be planted, nourished, tended to, cared for.  Yaakov was not concerned that some raw material would be lacking for the creation of the mishkan.  His concern was that the human effort to procure those materials would be lacking.  It is the toil and effort, the preparation that goes into making something from the earliest stages, which is what sanctifies the outcome. The gemara (B"M 85) tells us that R' Chiya trapped animals, made parchment, and wrote the scrolls that he then used for teaching Torah. He could have bought the parchment in a stationary store, but R' Chiya knew that preparation done b'kedusha ensures an outcome of kedusha.  Therefore, he made the parchment himself.  Yaakov planted trees to allow his children to invest their efforts in their growth, to take a hand in the earliest preparations and toil to make the mishkan.  

The Torah describes the wood for the beams of the mishkan as "atzei shitim omdim."  Chazal learn from the word "omdim" that the beams had to be stood upright in the same way as they grew, "derech g'deilasan."  Achronim debate what the scope of this din is.  Some apply it very broadly to any cheftza shel mitzvah.  Some go far as to say that if you hold a branch of a hadas upside down, for example, you can't say the bracha of "borei atzei besamim" on it because an eitz that is not held derech g'deilasan is not an eitz.  Meshech Chochma narrows the scope.  He is medayek that this requirement of "omdim" is mentioned only in connection with the beams, but not in connection with the aron or mizbeyach, which also were made of wood, and therefore writes that it does not even apply to all the kelim in the mishkan.  Why the difference?  He explains that the mishkan was dismantled when the camp moved; the beams had to be taken down and then put back up.  The aron and mizbeyach were never broken apart and put back together.  Once assembled, they remained as-is.  The din of derech g'deilasan only applies to things that are constantly being re-constructed or moved, not to things in a static state.

With this he explains the view of the Tur that there is no din of derech g'deilsasan for walls of a sukkah -- you don't have to ensure each year that the sukkah wall is always stood with the same side up.  Shibolei haLeket writes that it is better to do so.  The Tur disagrees because derech g'deilsasan does not apply to sukkah which is set up once and you are done for the week.  (The other view is interesting because the wall of a sukkah is not even a cheftza shel mitzvah.  The mitzvah is yeshivas sukkah, not building a sukkah.)

R' Noson Gestetner ties together the machshava idea behind Yaakov's planting of the trees that we started with with this din of derech g'deilasan.  Yaakov planted trees because trees grow and change and need our care.  It is that precisely items that are not static -- beams that are taken apart, a lulav and esrog that we pick up and put down --  where the din of derech g'deilasan applies.