'þæt' - M&R correctly observe that this second 'þæt' will present problems when translating. It is presented as an example of 'anticipation' in Old English, wherein the poet uses the pronoun 'þæt' to anticipate a noun clause. One comes away with the feeling that this is a clumsy construction! A modern reader may feel more comfortable with changing the second 'þæt' to the abbreviation 'i.e.' or to something like 'that is to say'. To find out more about this see M&R p. 66 (§148).