This is a good question. There are some odd Christian quotations and allusions in Beowulf. For instance, Grendel was supposed to be from the line of Cain. If you recall, Cain was the son of Adam and Eve, who killed his brother Abel in the Bible.
This allusion and others in the work show two points. First, it shows that during the composition of Beowulf, Christianity was a real force in the culture. Good and evil, for example, are couched in terms of the Bible and the lineage or genealogy of the Bible. From this point of view, the Bible has shaped the worldview to a certain extent. So, we can say that the Germanic/Roman world has been Christianized.
Second, the warrior ethics of the work, which is opposed to the Bible in many ways shows that Christinanity has beeen Romanized and Germanized. In short, what we are seeing is culture that is an amalgamation of various cultures and ideologies.