Its first occurrence in Exodus 12:15 significantly marks it as something to be "put away." There is no dispute as to the meaning of the word, which is sour or fermenting dough. The difference lies in its interpretation. This can be gathered only from its usage by the Holy Spirit.
 1.  It is used of its work in permeating the whole of that with which it is mixed (Matthew 13:33. Luke 13:21. 1Corinthians 5:6. Galatians 5:9. Hosea 7:4).
 2.  It is used of the bread which is made from the meal so permeated (Exodus 12:15, 19, 20, 34, 39; 13:7).
 3.  It is used in connection with sacrifices, as never to be offered to God with any offering made by fire (Leviticus 2:11; 6:17; 10:12).

 4.  It is used by Metaphor (see Appendix 6) for doctrine (Matthew 16:12. Mark 8:15. Luke 12:1. Galatians 5:9).
 5.  It is used of the effects of evildoers (1Corinthians 5:6‑8; 15:33).
 6.  In Leviticus 23:17 it is used in that which symbolizes mankind, and in a proper sense of being corrupted. The sin-offering associated with the leaven in the two wave-loaves corresponds with this.
 7.  In Amos 4:4, 5 it is either the language or Figure of Irony (see Appendix 6); or, it shows that the "thanksgiving with leaven" is symbolical of the sin which is ever present even in the worshippers of God.
  Thus in every instance, it is associated with, and symbolical of, only that which is evil.