כי היום ה' נראה אליכם, it had already become manifest as an appreciation of their handiwork when we read that the Presence (glory) of the Lord filled the Tabernacle (Exodus 40,34). It is therefore no more than appropriate that you express your appreciation of this by this sacrifice.

זה הדבר אשר צוה ה' חעשו, to place the weight of your body with your hands on the sin offering as well as on the burnt offering intended on behalf of the congregation.

'וירא אליכם כבוד ה, in addition to the manifestation of G’d’s presence already experienced by the Presence of G’d filling the Tabernacle. (compare verse 23)

וימציאו, they used this opportunity to become trained in the priestly functions by assisting in their father’s personal sacrifice.

כראשון, which had been burned although it had been a sin offering whose blood was destined for the altar in the courtyard.

כמשפט, that Aaron’s sons did the sprinkling of the blood, arranged the pieces of flesh and burned them.

מלבד עולת הבקר, apart from the gift offering which accompanied the morning burnt offering.

וימציאו, they also trained in performing the rites of the peace offerings offered on behalf of the congregation.