Penelope not only desires to offer hospitality to the stranger (as ancient Greeks permanently kept in mind that gods liked to mask), but she also wants to reestablish last bits of instruction by representatively placing the beggar, as a visitor, next to her son. The beggar is being ill-treated and hit out by the suitors, so this action means that she is still the presenter and young Telemachus the host, and their discussion is important. Moreover, the beggar is filthy, old and in rags, while the suitors are fresh, amusing, attractively dressed, and decent - but then again still no one of them is given the righteousness of sitting next to Telemachus. This would perhaps have the effect of putting the suitors down because of their rudeness.
