In "Game of Thrones" Season 7 Episode 6, we saw Jon Snow and his crew on a seemingly pointless mission beyond the Wall. The idea behind this was to capture a wight and then bring it to Cersei Lannister as proof that the Army of the Dead exists. But Cersei being, well - Cersei, ended up betraying their cause and, as a result, we'll see the Golden Company in Westeros next season to fight whatever is left of Daenerys' forces.
Given everything that happened in this episode, it's safe to say that the mission was an utter failure. The Night King ended up with a dragon of his own, the Wall is no longer an obstacle, and he has an entire continent full of dead bodies ready to be raised as wights. The Night King is winning, and his actions so far seem to suggest that he is somehow orchestrating the events to ensure the ultimate victory over mankind. Not only is there a plan, but Reddit user The Stark of Dorne adds an extra layer of tinfoil to this theory by stating that The Night King can send visions.
The theory
According to this theory, it is the Night King, also known as the Great Other who sends the visions and not the Lord of Light.
After all, everything that happened because of the so-called Lord of Light led the continent further into conflict. As a result, there are hundreds of thousands of dead bodies in Westeros at the Night King's disposal.
Let's just look at the War of the Five Kings. If it weren't for the Lord of Light, Renly would still be alive, and he and Stannis would have a chance to overcome their differences and attack King's Landing at full force, thus ending the war quickly. And if that wasn't bad enough already, the Lord of Light led Stannis to the North. The result? Even more dead bodies for the Night King. No surprise there.
Latest events
In "Game of Thrones" Season 7 premiere, the Hound saw the mountain shaped like an arrowhead in flames.
And in episode 6, this mountain just happened to be the same place where the crew ran into the Army of the Dead. How convenient for the Night King. Then, he just needed to wait for Daenerys to show up with her dragons, so he could kill one of them and acquire the one thing that will allow him to cross the Wall.
As far as Jon Snow's resurrection is concerned, this theory states that the Night King had a hand in this as well, because Jon is the only one who can convince Daenerys to go beyond the Wall with the dragons. In the end, Daenerys didn't need any convincing as she fell in love with Jon. Either way, the Night King got what he wanted.