There is a most peculiar mitzvah in Parshas Shoftim: “You shall not erect for yourselves a pillar (a matzeva), which Hashem your G-d hates.” The context makes it clear that the problem is not the building of a structure itself, but specifically building it as a religious object, a way to worship Hashem. Pillars can be understood as the obelisks from the ancient world, like the one from ancient Egypt shown on the right (they all look alike – a straight tower with a pointy top). Obelisks were popular in the ancient world – so popular in Rome, for example, that the Romans imported and rebuilt Egyptian obelisks in Rome – at the height of the Roman Empire there twice as many Egyptian obelisks in Rome than in Egypt!
Why does G-d so dislike pillars that they inspire hatred?
One possible answer is that building a pillar betrays a fundamental misunderstanding of the relationship between man and G-d. This relationship, at its most intimate, is supposed to be like the relationship between man and woman. G-d’s love for us is like marital love: the Torah is full of such imagery, with Shir HaShirim the most explicit of these. But who is the man, and who is the woman?
Rabbi Eitan Webb points out that the language is consistent: Hashem’s is the masculine role, that of the giver, and the Jewish people have the feminine role, welcoming and receiving Hashem.
So when worshipping Hashem, establishing a pillar, a phallic symbol like no other, shows a profound confusion about the nature of the relationship between man and G-d. It is forbidden because building a devotional pillar is a perversion.
But there are deeper reasons. To find them we have to go back to first principles: what is the purpose of our existence? The short answer is that Jews are meant to complete the completion of the world, specifically by healing the divisions Hashem made when he separated the light and the dark, and the waters above and below. These are the same divisions that Adam and Chava became aware of when they ate of the Fruit of Knowledge of Good and Evil. G-d made the world of divided and irreconciled elements, and it is our job to find good, holy ways to reunify all these dichotomies: Jacob and Esau, man and woman, man and G-d, and heaven and earth.
Of these, the last is most fundamental. We are meant to admix the physical world and the spiritual world, combining them in holiness. To do this, among other things, we use words to say blessings, to thank Hashem for even the smallest physical gratifications. We dip ourselves in the water of the mikva to achieve a spiritual purity. Our souls combine with our bodies and work to fulfill G-d’s will. For all mitzvos, the spiritual and the physical must work together, and not independently. Just as we are not allowed to take the spiritual path, and separate our souls from our bodies in a mystic quest, we are equally forbidden to exist solely in the physical plane, acting only upon instinct and desires. We must always strive to fuse the two.
This explains why building a pillar is not acceptable. A pillar is just rock. Like the Tower of Bavel, it is a high structure pointing up to the heavens, but there is no spiritual component whatsoever. And like the Tower of Bavel, it is unacceptable in G-d’s eyes. Even symbolically, (and skyscrapers notwithstanding) we must never think that our goal is to reach the heavens by building towers that pierce the skies.
The obvious contrast, of course, is with an altar (mizbeach). Altars are part and parcel of the Torah – all the forefathers built them and made offerings on them, as did the Jewish people in the desert and in Israel. A mizbeach is similar to a matzeivoh, in that both are devotional structures, and both are made out of stone. But the difference is that in a mizbeach, an offering is made, so on top of the earth, there is a sacrifice (which was a living thing), and that is consumed in turn by fire. The resulting smoke blows up toward the heavens, an acceptable combination of matter and energy representing the melding of heavenly and earthly elements together, “a sweet savor unto the Lord.”
 Except, Rabbi Webb points out, in the Beis Hamikdash, where the roles are reversed, and Hashem’s Shechinah is in the feminine. (The Beis Hamikdash is the exception, and is not in any event a place where all Jews can have the same relationship as the Cohenim.)
 But didn’t our forefather set up matzevos as well? Rashi, in Parshas Shoftim, says that our forefathers erected Matzevos, but I do not see any references except to three incidences by Yaakov: Once was to mark the division between Lavan and himself, so it served a legal and not a religious function. Once was to mark the place Rachel was buried, so it served the same function as do the matzevos (tombstones) that we erect today.
And the third is when Yaakov, on his way out of Israel, set up a matzevo on the place where he had dreamed of the angels on ladders, to mark the spot as holy, and to commemorate his vow to build a house of G-d (a vow that Hashem reminds him of, but he never fulfills). In this case it is clear that Yaakov aimed only to mark the spot, so that he (and others) would be able to use it to build a home for Hashem in the future. The highly spiritual nature of Yaakov’s vow in this episode may provide some counterweight to the fact of the physical matzevo itself. Additionally, I understand that Yaakov built a matzevo and not a mizbeach because he lacked anything to offer as a korban offering.