It is telling that Linnet would insist on Egypt as the place for their honeymoon, since that’s the same place that Jacqueline and Simon had originally planned to go for their honeymoon. This hints that Linnet may have had ulterior motives in marrying Simon, and that she wanted to hurt Jacqueline by making her feel replaced. Poirot, meanwhile, draws attention to the fact that all the characters he’s just spoken with have their own agendas, and that the real version of the truth probably doesn’t line up exactly with any of them.