You don't know what Messi and Argentina have agreed on.
I could care less what they've agreed on, Messi is contracted to Barcelona, not Argentina, and if he's resting then he shouldn't be on the bench at all, it's the final game of the season.
The bigger question is why he was left out completely in the last match, the unbeaten record went and now he's back to sit on the bench for what is now a pretty pointless match.
Utterly pathetic. Valverde is an awful manager and I hope he gets given his marching orders in the summer, or you can expect more mediocrity whenever Messi isn't there to bail his ass out.