The figure of Queen Wealtheow is an example of an archetype in Anglo-Saxon and other Germanic literature: she is a peaceweaver figure, fulfilling one of the most important roles of noblewomen in this era. As peaceweaver, it is her responsibility to take charge of the various rituals which maintain order between different groups of people, or tribes. The drinking cup, which she passes between the two groups, is part of this ceremonial behavior. By drinking from the same cup, the two groups of people are declaring that they are of the same tribe for the duration of whatever is currently happening: they are expressing a bond of fealty between the two groups. When a woman offers the cup, the element of overt threat is eradicated. Wealtheow is acting on behalf of her husband, but because she is a woman, she is a sort of neutral choice of cup-bearer.
We can see evidence of this kind of ceremonial cup-sharing in Germanic society going back to Tacitus's records from several centuries earlier. It is a significant part of the Germanic heroic society in which Beowulf is set.