Aharon was ordered by HaShem to take neither the time nor the actions to grieve for the boys (his sons), but rather continue with the service of the tabernacle. The joy of the Shekinah -- G-d's Glory/Presence with Israel was a much bigger picture than the loss of his own sons. Aharon felt it was hypocritical to "eat the sacrifice with joy", he ordered his portion to be included with the burned portion. Mosheh felt Aharon was wrong, but accepted his brother's decision.
I meditate omit all day.
I am wiser than my foes,
Because Your mitzvot are mine forever.
I have more understanding than all my teachers,
Because I meditate on Your instructions."