Are you sure you mean "poem." The most famous passage from Bede concerning a sparrow is the one below, from his Ecclesiastical History of the English People:
Talis...mihi uidetur, rex, vita hominum praesens in terris, ad conparationem eius, quod nobis incertum est, temporis, quale cum te residente ad caenam cum ducibus ac ministris tuis tempore brumali, accenso quidem foco in medio, et calido effecto caenaculo, furentibus autem foris per omnia turbinibus hiemalium pluviarum vel nivium, adveniens unus passeium domum citissime pervolaverit; qui cum per unum ostium ingrediens, mox per aliud exierit. Ipso quidem tempore, quo intus est, hiemis tempestate non tangitur, sed tamen parvissimo spatio serenitatis ad momentum excurso, mox de hieme in hiemem regrediens, tuis oculis elabitur. Ita haec vita hominum ad modicum apparet; quid autem sequatur, quidue praecesserit, prorsus ignoramus. Unde si haec nova doctrina certius aliquid attulit, merito esse sequenda videtur.
- Translation: The present life of man, O king, seems to me, in comparison of that time which is unknown to us, like to the swift flight of a sparrow through the room wherein you sit at supper in winter, with your commanders and ministers, and a good fire in the midst, whilst the storms of rain and snow prevail abroad; the sparrow, I say, flying in at one door, and immediately out at another, whilst he is within, is safe from the wintry storm; but after a short space of fair weather, he immediately vanishes out of your sight, into the dark winter from which he had emerged. So this life of man appears for a short space, but of what went before, or what is to follow, we are utterly ignorant. If, therefore, this new doctrine contains something more certain, it seems justly to deserve to be followed.
A rhetorical analysis of this passage might focus on the way the speaker begins by showing respect to the king; the use of the famous simile; the fact that the simile is extended and developed; and the way the speaker identifies himself with the rest of humanity by using the word "we." Finally, the speaker concludes on a very reasonable not, especially by beginning the final sentence with the words "If, therefore" and by later using the words "it seems." The speaker thereby makes himself sound like a thoughtful, reasonable, logical person.
The dominant rhetorical device in this text is the metaphor of life as a sparrow flight through a mead hall. It is interesting because it casts life as a brief moment of safety from uncertainty, which is different than how later Christian thinkers would interpret it. The rain, wind, and snow are outside the building, and by flying through the sparrow is momentarily shielded. Christianity, or at least the particular kind of Christianity Bede is promoting (the work is largely a description of conflicts between the numerous variants of Christianity in England) is the way to deal with what is out of doors.
In thinking of Bede's Sparrow parable, we should wonder (expanding on #5) why the safety and security are inside the hall, in sinful life, instead of outside it in the glory of heaven and God's countenance? I would think a better religious allegory would be the sparrow flying from sunshine through a thunderstorm, and then out the other side into sunshine again. However, since no man wants to die, despite what may lie on the other side, we could also interpret the shock of leaving the warm hall as the shock of death; what comes after is uncertain.
Rhetorical devices that are key to this text are of course the famous analogy that is drawn between human life and the life of a sparrow fluttering through the hall. Bede's point is to try and make us see how ephemeral and temporary our lives are in the large scheme of things, and thus his rhetorical devices are designed to support this.