Verse 12 mentions the offering of the firstfruits, which is a reference to the Pentecost loaves. The Pentecost grain offering contains leavening, while the typical grain offering here does not. God forbids the priest from putting the loaves on the altar because of the leavening.
The altar symbolizes God's table, and He does not partake of the leavening. Instead of being burned on the altar, the priest holds up the loaves before God and waves them. That action implies God's close inspection, and hopefully, His acceptance. But the leavened grain offering is for use by the priest. It is acceptable for one use, but not another. If the leavening typified something positive in the Pentecost offering, it would have been fit for God's altar. However, as this shows, God requires a distance from the leavening.
