It's a whole new card out there, or at least it will be whenever a card is Revived or Recalled. You might want a quick refresher as to what Recall does, or how it can affect a card (like in Katarina's case) before reading this article.
Think of Recall and Revive as a clean slate. Any buffs or status effects all go out the window when a unit is recalled or revived. When employing either keyword, you are essentially creating a new version of that unit.
Let's take a look at this in action. Here we have a Solitary Monk:
When she's on the board, all allies are Recalled back to your hand as soon as she is played. That means any buffs you've placed upon other allies are wiped clean. While that can be a bit of a strategic blow, it can also get your units out of harm's way.
Frustrated at the sweeping save you've just employed, your opponent decides they want Solitary Monk for themselves.
Your enemy now has your Solitary Monk thanks to the clever machinations of a well-timed Possession. Complete ownership belongs to your opponent. In a truly big-brain move, your opponent summons Chronicler of Ruin using your Solitary Monk as fodder (rude!)
As the Chronicler of Ruin revives an ally (and as we mentioned before, this mechanic is essentially summoning a new copy of that card), the Solitary Monk remains in your opponent's care. Frustrating, right? That's the power of Revive and Recall. Use both to your advantage in the matches to come (before your opponent does).