In the Haggadah you will find the following exegesis of part of Deuteronomy 26:8:
וּבִזְרֹעַ נְטוּיָה. זוֹ הַחֶרֶב, כְּמָה שֶּׁנֶּאֱמַר: וְחַרְבּוֹ שְׁלוּפָה בְּיָדוֹ, נְטוּיָה עַל-יְרוּשָלָיִם..
"And with an outstretched forearm" - this [refers to] the sword, as it is stated (I Chronicles 21:16); "And his sword was drawn in his hand, leaning over Jerusalem:
What is the sword that is referred to? The only references to swords I can see in Exodus are 5:3, 5:21 and 18:4 and all of those are threats of sword-use against the Jews. How did God use a sword with his outstretched arm to help redeem the Jewish slaves (recall we are expounding the phrase "[God took us out] with an outstretched arm")?
Why are we referencing such a seemingly unrelated part of Tanakh? The story of the plague following King David's census seems completely unrelated to the Exodus. Is there a thematic connection?
I note the phrase "חרבו שלופה בידו drawn sword in his hand" shows up exactly two other places in Tanakh (Numbers 22:23 and Joshua 5:13) also seemingly unrelated to the Exodus.