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)

4121. 'And he took his brothers with him' means forms of good replacing those which it had lost. This is clear from the meaning of 'brothers' as forms of good, dealt with in 2360, 3160, 3303, 3459, 3803, 3815. In the internal sense 'brothers' means people who are governed by the same kind of goodness and truth, that is, they share the same affection for these. Indeed all in the next life are grouped together in different communities on the basis of their affections; and those so grouped together in any community constitute a brotherhood. They do so not because they call themselves brothers but because they are such through their being joined to one another. In the next life it is goodness and truth that lie behind that which on earth is called a blood-relationship and a relationship by marriage, and for this reason the latter correspond to that goodness and truth. Indeed regarded in themselves forms of goodness and truth acknowledge no other father than the Lord, for they exist from Him alone, and therefore all who are governed by forms of goodness and truth exist in a brotherly relationship with one another. Yet degrees of affinity exist, determined by the particular nature of each form of goodness or truth. In the Word these degrees are meant by brothers, sisters, sons-in-law, daughters-in-law, grandsons, granddaughters, and many other names for relatives in a family.

[2] On earth however these names are given to people because they have the same parents, no matter how much these people differ from one another in affection. But that kind of brotherly relationship and affinity is dissolved in the next life, and unless on earth they have been governed by the same affection they all enter different brotherly relationships. Such people, it is true, do as a general rule come together initially, but in a short while they are parted. For in the next life it is not money that holds people together but, as has been stated, affections, the nature of which are plain to see as if in clear daylight, as also is the nature of the affection which one person has had for another. Since affections are so plain to see there, and since everyone's affection attracts him towards the community that is his, the association with one another of people whose mental dispositions have not been in agreement is therefore broken. In that case all ties of brotherly relationship and of friendship possessed by the external man are eliminated in both parties, while those which had existed with the internal man remain. The reason why 'he took his brothers with him' means forms of good replacing those which it had lost is that when one community is being separated from another, as stated above in 4077, 4110, 4111, it moves towards another and so towards other forms of good which replace the former.