parshanut torah comment - Why is every commandment and action in regards to the 10 plagues repeated?

When we read about the 10 plagues everything is repeated twice: once when Hashem commands Moshe and a second time when Moshe executes the plague. The Torah could simply write "and he did so" after each ויאמר ה׳ אל משה (and Hashem said to Moshe) occurrence. Why repeat?