Deuteronomy 6:4

שְׁמַע יִשְׂרָאֵל ה' אֱלֹקֵינוּ ה' אֶחָד

Hear, O Israel, the L-rd is our G-d, the L-rd is One.

The letter ayin of the word “Shema” (“hear”) is written oversized, as is the letter daled of the word “echad” (“one”). The commentators provide a number of explanations as to why this is. The Midrash in Leviticus Rabbah 19:2 points out that the oversized daled of echad shares a reciprocal relationship with the oversized letter reish in Exodus 34:14, that one may not bow to any other “god.” (“Other” is “acheir” in Hebrew.) The letters daled and reish look similar so they are written oversized to prevent mistakes. If one were to accidentally read Shema (our verse) to say that there is another “god,” or if one were to misread the verse in Exodus 34 to prohibit serving the One G-d, the results would be disastrous!