Since Pharaoh was giving them animals for Korbanos, why did they need to take their own, if they were going only for three days?
Riva: Moshe meant that Yisrael will take from their own animals to serve Hashem - to offer as Korbanos; and that they would also take from Pharaoh, since they did not know how many Korbanos they will require we until they arrive there.
Abarbanel (to 10:21): Moshe said in astonishment, "Atah Titen b'Yadeinu... v'Asinu La'Hashem'?! We will not take your animals to offer them, therefore, we must take ours! And "v'Gam Mikneinu" is like 'Aval Mikneinu.'
Yashresh Ya'akov: Refer to 10:25:1:3.
QUESTIONS ON RASHI
Rashi writes: "'Mah Na'avod' - I.e., how intense the service will be." What is Rashi explaining?
Gur Aryeh: We did know the correct method of service before Hashem - the Zevichah of animals as sacrifices. (This had been their request of Pharaoh from the outset, see 5:3). What we did not know yet, was the amount of animals that would be required.
