For something to be "unleavened" means that it's been made without yeast. Since yeast is what makes bread rise and take on its airy texture, unleavened bread is relatively flat, dense and hard. The idea that unleavened bread is holy appears in both the Old and New Testaments and is still part of both Jewish and Christian traditions.

In the Word, bread represents the desire for what is good -- which gives us spiritual energy, just as bread gives us natural energy. Yeast, meanwhile, represents falsity -- so that bread made without yeast is a pure desire for good, free of falsity. This also makes sense because air represents our capacity to understand what's true -- which is the same capacity we use to embrace ideas that are false. Yeast causes bread to rise by producing gases as it ferments, thus adding "bad" air to the bread.

357. 'Cain's anger was set ablaze' means that charity had departed. This becomes clear from what comes further on, where it is said that he killed Abel his brother, who means charity. Anger is the general emotion that results from anything which gets in the way of self-love and its desires. In the world of evil spirits this is perceived plainly. Indeed general anger against the Lord prevails, because they are not moved at all by charity, but only by hatred. Anything that is unfavourable to self-love and the love of the world arouses opposition, which manifests itself in anger. In the Word, anger, wrath, and even rage, are frequently attributed to Jehovah; but in fact they belong to man and are attributed to Jehovah because they seem to be from Him, for reasons mentioned already. The following is stated in David,

He let loose on them His fierce anger and wrath, and rage, and distress, and a mission of evil angels. He levelled out a path for His anger, He did not spare their soul from death. Psalms 78:49-50.

Not that Jehovah ever 'lets loose His anger on anyone', but that people bring it down on themselves. Nor, as it is said, does He send evil angels but man takes them to himself. This is why the statement is added that 'He levels out a path for His anger and does not spare their soul from death', and it is said in Isaiah that

He will come to Jehovah, and all will be ashamed who were incensed against Isaiah 45:14.

From these quotations it is clear that 'anger' means evils, or what amounts to the same, a departure from charity.