Adam Clarke on Exodus 29:39

One lamb thou shalt offer in the morning - These two lambs, one in the morning, and the other in the evening, were generally termed the morning and evening daily sacrifices, and were offered from the time of their settlement in the promised land to the destruction of Jerusalem by the Romans. The use of these sacrifices according to the Jews was this: "The morning sacrifice made atonement for the sins committed in the night, and the evening sacrifice expiated the sins committed during the day."