In Exodus 2:4, 7, Miriam signifies the truth of the church at that time and the religion near them. (Arcana Coelestia 6727, 6739)

In Exodus 15:20, this signifies the glorification of the Lord from the good of faith with reciprocity. (Arcana Coelestia 8337, 8340) When men represent truth, the women related to them represent good. Here Miriam represents external good, and so she is called the sister of Aaron, not the sister of Moses. (Arcana Coelestia 8337)

6727. 'And his sister stood at a distance, to know what would happen to him' means the Church's truth far away from there, and observation. This is clear from the meaning of 'sister' as rational truth, dealt with in 1495, 2508, 2524, 2556, 3160, 3386, thus the Church's truth, for this is rational truth; and from the meaning of 'to know what would happen' as observation.