"They made the planks of the Tabernacle of acacia wood, upright." Rabbi Halifa of Kasrin said, "The Holy One Blessed Be He taught derekh eretz with this commandment, that if a person requested to build a home out of fruit trees, one could say to them, 'And what did the King of Kings, the Holy One Blessed Be God, that everything is God's, when God asked for a Tabernacle to be built, God ignored fruit trees, and so, all the more so, should you.'"
"You are what you eat," as the old adage goes—but according to this midrash, you are also what you build, or more precisely, you are how you build. The midrash cited above seeks to answer the question of why God chose the wood from the acacia tree as the core component for the construction of the Mishkan, the movable Temple the Israelites worshipped in while wandering the desert. In the eyes of the midrash, acacia wood is a humble wood, inexpensive wood. God commanded the Mishkan to be made of acacia to teach principles of derekh eretz—that is, the traits one should embody, in this case humility.
In the second part of the midrash, a person is admonished for wanting to use the wood of fruit trees to build a home, this wood apparently being a symbol of arrogance. But why does the midrash choose fruit trees and not another type of expensive wood? It would make sense to use cedar or cypress wood, woods the Torah describes as being used in construction, as examples of luxurious building materials. By using fruit trees, the midrash is teaching a subtle lesson about our personal responsibility for the resources we use. It is not just that the wood from fruit trees is expensive, it also is an important food source. The cutting down of many fruit trees to build homes for wealthy members of a community might lead to food insecurity for more vulnerable members.
The midrash assumes that we need to use and consume natural resources. This fact is woven into the very fabric of our relationship to both God and the world. The Torah commands the Israelites to build a Mishkan out of various resources, abundant and limited. But the derekh eretz that this midrash teaches in addition to humility is that we are responsible for the impact of our consumption, and that our use of natural resources must be done in a manner that conveys both humility and compassion.