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.

6959. 'And Jehovah said further to him' means foresight of what those who belonged to the spiritual Church were going to be like if they were not in possession of faith. This is clear from the meaning of 'Jehovah said' as foresight, as above in 6946. The reason it means that this future was foreseen - what those who belonged to the spiritual Church would be like if they were not in possession of faith - lies in the words that immediately follow. These deal with members of the spiritual Church, represented by 'the children of Israel', describing what they were going to be like if they did not possess faith, that they would become profaners of truth. For the first miracle in which the rod became a serpent means their state, a state in which they would become wholly sensory- and bodily-minded; the present miracle in which Moses' hand became leprous means profanation since this would come next if that Church continued to be devoid of faith.

[2] In childhood, and after that in adolescence, those who belong to the spiritual Church possess faith in the things taught by their Church. But during those years the faith they possess is obtained from parents and teachers, not by their own efforts. If therefore they subsequently give up that faith they can profane truth only to a small extent, and Divine means can be used to remove that profanation, thereby freeing a person from guilt on account of it. But if a person possesses faith in what the Church teaches and in the Word as a result of his own efforts, that is, he confirms for himself what he has been taught, but after that gives it up and refuses to accept what he has previously believed - and especially if he leads a life that goes against the truth he has confirmed for himself, and either explains it to suit himself or totally rejects it - he renders truth profane. The reason why is that within himself he mixes up and joins together truth and falsity. Because people like this have scarcely any remnants of what is true and good they come at length in the next life to be like skeletons, having as little life left as one's bones possess in comparison with the organic life of the flesh. A more direful lot however awaits those who render good profane than those who render truth profane. Those belonging to the spiritual Church are able to profane truth, but they are less able to do the same thing to good.

[3] Since 'leprosy' means the profanation of truth and is referred to in what follows next, please see first what has been stated and shown already about profanation:

Those within the Church are capable of profaning holy things, but not those outside it, 2051, 3399.

Holy things cannot be profaned except by those who first acknowledge them, 3398.

People who do not know holy things, and also those who do not acknowledge them, cannot profane them, 1008, 1010, 1059, 3398, 4289.

It is also profanation when one acknowledges and believes truths and forms of good and yet leads a life that goes against them, 4601.

A person is withheld as far as is possible from profanation, 301-303, 1327, 1328, 3398, 3402.

The lot awaiting profaners is the worst of all in the next life, 6348.