Aaron was the brother of Moses. He symbolizes two things, at different stages of the story.

During the first part of the exodus, when he was Moses' spokesperson, Moses represents the Word as it truly is, as it is understood in heaven, while Aaron represents the Word in its external sense, as it is understood by people in the world. This is why Aaron talks for Moses, and the Lord says of him "he shall be as a mouth for you, and you shall be to him as God." (Exodus 4:16)

Later, after the Tabernacle was built and he was inaugurated as high priest (see Leviticus 8,9), Aaron represents the Lord as to the Divine Good, and Moses represents the Lord as to the Divine Truth.

In Exodus 28:1, Aaron signifies the conjunction of Divine Good with Divine Truth in the Divine Human of the Lord. (Arcana Coelestia 9806, 9936)

In Exodus 32:1, Aaron represents the external of the Word, of the church, and of worship, separate from the internal. (Arcana Coelestia 10397)

In Exodus 4:14, before he was initiated into the priesthood, Aaron represents the doctrine of good and truth. (Arcana Coelestia 6998)

7318. 'And the fish that are in the river will die' means that factual knowledge of truth will be destroyed. This is clear from the meaning of 'fish' as factual knowledge, dealt with in 40, 991, at this point factual knowledge of truth since it says that the fish are going to die because the water they are in has been turned into blood, meaning that such knowledge will be destroyed through falsification; and from the meaning of 'dying' as being destroyed. A number of examples will show what the falsification of truth is. Truth is falsified when on the basis of false reasonings people deduce and declare that because no one can do good all by himself good contributes nothing to salvation. Truth is also falsified when they declare that whatever good a person does has self in view and is done for the sake of reward, and this being so, that the works of charity do not need to be performed. Truth is falsified when people declare that because all good has its origin in the Lord a person should not perform anything good at all but should wait for inspiration. Truth is falsified when they declare that truth can exist with a person without the good of charity, thus faith without charity. Truth is falsified when people declare that nobody can enter heaven except him who is wretched and poor, and also when they declare that no one can enter unless he gives all his goods to the poor and reduces himself to a state of wretchedness.

[2] Truth is falsified when people declare that everyone, irrespective of the kind of life he has been leading, can by mercy be admitted into heaven. Truth is falsified further still when they declare that someone has been given the power to admit whomever he chooses into heaven. Truth is falsified when people declare that sins are altogether purged, and washed away like dirt by water. And truth is falsified further still when they declare that somebody has the power to forgive sins, and that when they have been forgiven those sins are altogether purged, making the person pure. Truth is falsified when people declare that the Lord has taken onto Himself and so bears all sins, so that a person can be saved no matter what kind of life he leads. Truth is falsified when they declare that no one is saved except him who is within the Church. The reasonings by means of which falsification is effected are contained in the notion that those who are within the Church have been baptized, possess the Word, know about the Lord, resurrection, eternal life, heaven, and hell, and accordingly know what the faith that enables them to be justified is. Reasonings like these are countless, for not one single truth exists that is incapable of being falsified, and there is no falsification that cannot be substantiated by means of reasonings based on illusions.