Firstly, the reunion highlights the theme of love. Gatsby has been in love with Daisy for years, and his desire to be reunited with her has been the driving force behind his accumulation of wealth and status. When they finally meet again, their love is rekindled, and they both feel a sense of joy and happiness that they have not experienced in a long time. However, their love is also complicated by the fact that Daisy is married, and their reunion raises questions about the morality of their relationship.
Secondly, the reunion also explores the theme of desire. Gatsby's desire for Daisy is all-consuming, and he has built his entire life around the hope of being reunited with her. When they finally meet again, their desire for each other is palpable, and they both feel a sense of longing and passion that they cannot ignore. However, their desire is also tempered by the reality of their situation, and they both struggle with the consequences of their actions.
Finally, the reunion also contributes to the exploration of identity. Gatsby has created a new identity for himself, one that is built around his wealth and status, in order to win Daisy's love. When they finally meet again, he is forced to confront the reality of his true identity and the fact that he can never truly escape his past. Daisy, too, is forced to confront her own identity and the choices that she has made in her life. Overall, the reunion between Gatsby and Daisy in chapter 5 is a crucial moment in the novel that explores themes such as love, desire, and identity. It highlights the complexities of human relationships and the ways in which our desires and identities shape our lives.