Rashi on Exodus 3:15/רש"י על שמות ג׳:ט״ו

1זה שמי לעלם THIS IS MY NAME FOR EVER — The last word is written without ו (so that it may be read לְעַלֵּם and it would mean “this is My Name which is to be concealed”) to suggest: Conceal it (this Divine Name), so that it shall not be read exactly as it is written (but should be read as אדני; cf. Pesachim 50a; Exodus Rabbah 3:7).

2וזה זכרי AND THIS IS MY MEMORIAL (the word may signify “the mention of Me”) — He taught him how the Divine Name should be read. So, too, did David say, (Psalms 135:13) “O Lord, Thy name is for ever (שמך לעולם), O Lord, Thy memorial is throughout all generations (זכרך לדר ודר).