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)

6982. 'I am not a man of words' means that he is lacking in speech. This is clear from the meaning of 'a man of words' as the fact that he is not an able speaker, and so is lacking in speech. What all this entails must be stated. The subject here in the highest sense is the Lord, for 'Moses' represents the Lord in respect of the law of God, thus in respect of God's truth. Truth that goes forth directly from the Divine cannot be heard by anyone, not even by any angel; if what is Divine is to be heard it must first be made human, and it is made human when it passes through the heavens. When it has passed through the heavens it is presented in a human form and becomes speech, speech which is uttered by spirits who, while they are in that state, are called the Holy Spirit. But the Holy Spirit is said to come forth from the Divine because what is holy with a spirit, namely the holy truth uttered by him at that time, comes forth from the Lord. From all this one may recognize that truth coming forth directly from the Divine cannot be presented to anyone as spoken word or speech except by means of the Holy Spirit. This is what is meant in the highest sense when Moses, who represents the Lord in respect of God's truth, says that he is 'not a man of words', and by the fact that Aaron his brother was to be attached to him; Aaron was to serve him in place of his mouth, and he was to serve Aaron in God's place.