ואם מזבח אבנים תעשה לי אל תבנה אתהן גזית
Rashi quotes the Mechilta where Rabbi Yishmael says: Every example of im (usually translated as if), in the Torah is referring to something which is optional, except for three times. The first of them is the above pasuk in which the im is not discretionary, but rather, translated as “when” you will build an Altar; the second instance (Shemos 22:4), is concerning lending money, im kessef talveh es ami, “if” you lend money, would be the incorrect translation since one must lend money. Hence, it is read “when” you will lend money. Last, is v’im takriv Minchas Bikurim (Vayikra 2:14);…
