Or HaChaim on Exodus 12:28/אור החיים על שמות י״ב:כ״ח

1 וילכו ויעשו בני ישראל כאשר צוה השם, The children of Israel went and did as G'd commanded, etc." The Torah had to repeat כן עשו, "they did so," to underline that they obeyed what Moses had commanded them in the name of G'd though they did not understand the meaning of all these regulations. Had the Torah not written the words כן עשו, we could have thought that they did so because they understood it all.