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)

4582. 'And poured oil onto it' means the Divine Good of love. This is clear from the meaning of 'oil' as the Divine Good of love, dealt with in 886, 3728. In the internal sense 'setting up a stone pillar, pouring out a drink-offering onto it, and pouring oil onto it' describes the process of progression from truth, as this exists in the ultimate degree, to truth and good that are more interior, and at length to the good of love. For 'a stone pillar' means truth as this exists in the ultimate degree of order, 4580; 'a drink-offering' means truth and good that are more interior, 4581; but 'oil' means the good of love. This was the nature of the process by which the Lord progressed when making Divine His Human; it is also the nature of the process by which man progresses when, through regeneration, the Lord makes him heaven-like.