A little known tidbit about the Oaths is that they're somewhat bugged. If you go from Shield oath to Sword oath you keep the emnity gains from Shield Oath.

There's a reddit post on the subject, but I and my friend have noticed it too. We used to think other tanks were bad because they couldn't keep emnity off of us, but it just turns out it's a bug.

You don't keep the damage reduction though.