YEAST
Substance used to ferment and raise dough (Ex. 12:15, 19; 13:7). In biblical times, a piece of sour dough was used for this. Leaven was prohibited in the offerings that were to be consumed on the altar; those in which they participated could have it (Ex. 7:13; 23:17).
Leaven, an agent of corruption, is the emblem of pernicious doctrines (Mt. 16:11; Mark 8:15), of evil (1 Cor. 5:6-8; Gal. 5:9), of that we have to keep ourselves totally.
During the Passover, the Israelites were not to consume leavened bread, nor even to have leaven in their homes, under penalty of being cut off from their people (Ex. 12:15, 19). The absence of yeast symbolized the purity that God demands of his servants.
This was also a reminder of their departure from Egypt, since the Israelites took the unfermented dough with them. The tastelessness of this unleavened bread would serve as a reminder of the afflictions of Egypt (Ex. 12:34, 39; Deut. 16:3; 1 Cor. 5:7, 8).
The parable of the leaven (Mt. 13:33) has been variously interpreted. Certain commentators have believed they see in it an image of the saturating influence of the Gospel that, in a perhaps hidden way, penetrates all media and the entire earth (cf. Col. 1:16).
However, it must be noted that in all other biblical passages leaven is consistently a symbol of iniquity. In the same way that the tares are mixed with the wheat until the harvest (Mt. 13:24-30), so the yeast introduced into the flour produces a leaven of corruption that will increase until the apostasy and the judgment that is to come. fall on it (Mt. 24:12; 2 Thes. 2:3).
In this sense it is used by Paul in 1 Cor. 5:6-8 and Gal. 5:9, so the optimistic interpretation is invalid. The parable of the tares and the parable of the leaven show different aspects of the same reality: the process of corruption leading to apostasy within the testimony of the Church on earth until the intervention of the Lord in judgment on an apostate Christianity (cf. Luke 18:8; 1 Tim. 4:1; 2 Tim. 3:1-5, etc.).
Thus, “until everything was leavened,” instead of meaning that the whole world will be won to the Gospel, has a diametrically opposite meaning.