God Mode is an incredibly powerful weapon in the arsenal of Person of Interest's main characters, and it can be initiated when they need help from the Machine. God Mode has been used a handful of times on the CBS series, during the protagonists' most desperate moments.
God Mode was one of several interesting features of the Machine, a highly advanced A.I. created by Harold Finch (Michael Emerson). Designed to prevent acts of terror, the Machine became a weapon for the government. Though it fell out Finch’s hands, a backdoor to the Machine installed by Nathan Ingram (Brett Cullen) gave Finch an opportunity to use its intel to stop murders before they could happen. One of the ways that it helped them when they needed it most was through the use of God Mode.
Introduced in the Person of Interest season 2 finale, God Mode is what happens when a character taps into the Machine, which can then relay information to the person they’re communicating with. Among the characters who have gone into God Mode are Reese (Jim Caviezel) and Root (Amy Acker). During this time, the Machine usually tells them what to do through an earpiece. Since the Machine “sees everything” through cameras, satellite feeds, GPS devices in phones, and more, the Machine can easily pinpoint the location of hostile targets. This way, the Machine can warn Reese when an enemy is approaching. Having the Machine keep an eye on his surroundings for him makes it easier for Reese to gun down a high number of enemies.
In God Mode, Reese can speak directly to the Machine and issue commands. For instance, in one scene Reese told it to disable the lights in the area, preventing his targets from knowing where he was. It's also worth noting that the Machine’s evil counterpart, Samaritan, has its own God Mode. In a season 4 episode, Root had an intense battle with Martine (Cara Buono), with both characters in God Mode during the fight.
God Mode is used only on rare occasions in Person of Interest. The first time it was accessed was a result of the Machine having to go into reset mode after being hit with a virus uploaded by Kara Stanton (Annie Parisse). After the reboot was finished, it became possible for one person to answer a phone call from the Machine and receive administrator access to the Machine for a period of 24 hours. Both Root and Reese picked up the line and were able to temporarily make use of God Mode. It was used again when it was deemed by the Machine that God Mode was needed to fight Samaritan.
God Mode would of course have been useful in other situations as well, but Finch never designed the Machine for this purpose, and never actually wanted anyone to have that much access to it. That being said, the Machine seemed to develop a mind of its own, thanks to Finch’s efforts to make sure it understood humanity. Because of that, the Machine was able to serve as a willing and capable ally throughout the show’s five-season run.