Analysis of information sources in references of the Wikipedia article "Tefillin" in English language version.
I think the beauty was important then because it reminded the people of the worth of God in their worship. During the dry and dusty days of desert wanderings, they needed a reminder of God's majesty.
Beauty enhances the mitzvot by appealing to the senses. Beautiful sounds and agreeable fragrances, tastes, textures, colors, and artistry contribute to human enjoyment of religious acts, and beauty itself takes on a religious dimension. The principle of enhancing a mitzvah through aesthetics is called Hiddur Mitzvah. The concept of Hiddur Mitzvahis derived from Rabbi Ishmael's comment on the verse, "This is my God and I will glorify Him" (Exodus 15:2):
{{cite book}}: CS1 maint: location missing publisher (link)Rav Shlomo Ha-kohen of Vilna, in his work of responsa Binyan Shlomo (siman 6), writes that he was once asked why the Gemara never mentions a requirement to purchase beautiful tefillin. Seemingly, tefillin is no less a religious article than a tallit, Sefer Torah or lulav, and thus the obligation of hiddur mitzva should apply equally to tefillin.
Rav Shlomo Ha-kohen of Vilna, in his work of responsa Binyan Shlomo (siman 6), writes that he was once asked why the Gemara never mentions a requirement to purchase beautiful tefillin. Seemingly, tefillin is no less a religious article than a tallit, Sefer Torah or lulav, and thus the obligation of hiddur mitzva should apply equally to tefillin.