If you can remember the fight Naruto had with Gaara during the point when Sasuke wanted to fight him but wasn’t able to because of his curse mark, then you’d know how fantastically epic that fight was. Also this image makes a lot more sense if you can remember that fight!
A reminder of that fight was that Gaara was pushed into bringing his Tailed Beast out, this meant that Gaara had to go into a deep sleep, referring to the title of the image. Once Gaara went to sleep, the Tailed Beast, Shukaku would take over his own body and use it to its fullest potential, he would be able to do anything he wanted. This lead to a fantastic battle between them!
The awesome image was drawn by Katakiari, she’s got some other fantastic fan art of other Naruto characters which you should definitely check!