Rashi on Exodus 4:21/רש"י על שמות ד׳:כ״א

1בלכתך לשוב מצרימה וגו׳ WHEN THOU GOEST TO RETURN TO EGYPT, [SEE THAT THOU DO etc.] — Understand that you should go thither with this purpose in mind: that you should be vigorous in carrying out my mission — to do all my wonders before Pharaoh and that you should not be afraid of him.

2אשר שמתי בידך [THE WONDERS] WHICH I HAVE PUT IN THY HAND — Not in reference to the three signs mentioned above was God speaking, for he had not commanded him to do these before Pharaoh, but before Israel in order that they might believe in him, nor do we find that he did them before him. But God meant: those wonders which I shall in future place in thy hand in Egypt — such as (Exodus 7:9) “When Pharaoh shall speak unto you, [saying, show a wonder (מופת) for yourselves]”. Do not be puzzled because it is written אשר שמתי (a past tense), for the following is what it means: when you will be speaking with him I shall already have put them into thy hand.