leaven: The bread eaten in biblical times was like modern sourdough. What is often called leaven was wild yeast spores mixed into moist dough or flour. The leaven would grow, fermenting and becoming sour and raising the dough. They would save a portion of this sour dough to knead into future batches (Matthew 13:33).
Unleavened bread was necessary for Passover (Exodus 12:8). This was to remember Israel's slavery in Egypt (Deuteronomy 16:3) and their quick departure (Exodus 12:34; 13:3). After the exodus, unleavened bread became altar bread. They could not burn leavened bread on the altar.
honey: The Hebrew word debash may also mean "fruit nectar." It is unknown why they did not burn it. But it might relate to its use in pagan offerings, especially to underworld gods. If it means "fruit nectar," its link with wine and fermentation might have connected it with leaven, making it unsuitable for the altar.
Yet, they could use both honey and yeast in first crop offerings (Leviticus 2:12). They would present loaves made with leaven with thank offerings (7:13). They gave them to the priest during the Festival of Harvest (23:17).
In the New Testament, leaven becomes a spiritual symbol, highlighting its sour taste and how it spreads (Matthew 16:6, 11, 12; 1 Corinthians 5:6–8; see also Matthew 13:33).