Jesus warned His disciples to beware of teachings from Pharisees that He called “leaven,” (Matthew 16:5-12). Leaven is yeast, or some similar agent of fermentation, like malt. It creates gas.
In Matthew 13:52, He told them that someone who had knowledge of Scripture and gained knowledge of the Kingdom was like a landowner (prestigious and wealthy) who could bring things of value that were both old and new from his storehouse. The old has one value, the new has another. John the Baptist only had the old, and could not recognize the new (Luke 7:11-19).
Leaven swells things up with gas. The Holy Spirit fills things up with Life.
Knowledge puffs up, but love builds up (1 Corinthians 8:1).