Again, Telemachus uses the (elided) formal address of ξεῖν᾽ referring to Athena/Mentes status as a guest-friend. What Telemachus answers here only really makes sense if one realizes the sacredness of that status. The need of Telemachus as a host to perform the duties to a guest-friend are if anything more important given that Athena/Mentes’ speech which just ended referred to Zeus as her father in such a way as to make the identity as Athena of Athena/Mentes clear. After all, by honoring the guest-friend in ancient Greek society, one would also honor the gods— especially including Zeus. Thus Telemachus thanks Athena/Mentes for the concern for a father and son, i.e., Telemachus himself and Odysseus, but says that before they go (thereby accepting Athena/Mentes’ plan implicitly) they should wait while Athena/Mentes washes, especially the hands. Washing, especially of the hands, was the most basic amenity traditionally offered to a guest-friend.
N.B.: I’ve included a picture from an on-line game in which Telemachus is a character. He does not look very Greek in any way, but the picture is still a modern representation of him.