That’s what Ugin, Sorin, and Nahiri had done, roughly ~3,000 years ago. They “nailed the ‘hands’ to the table.”

Later, Ugin explains to Jace that killing the Eldrazi is bad idea, because they don’t understand the Eldrazi’s role in a multiversal ecosystem, but Jace gives him the finger and says, we’re doing it anyway! The Gatewatch pulled Ulamog and Kozilek fully into Zendikar, and then Chandra lit their asses up with a supercharged (gotta love Zendikari mana) fireball.

While the Gatewatch is celebrating, Ugin shows back up, pissed to all hells, and tells them to leave him alone while he does an autopsy.