I just moved into a new house and am unable to close my gate because there is something nailed to the ground at the threshold that is sticking up too high for the gate the close. Any idea what this thing is? I'm trying to decide if I just remove it to allow the gate to close or if I need to keep it there and bury it a little deeper.
That is called Paver Edging. It is used to keep the pavers tight or to separate one section from the other. It's usually covered to the point that you only see a small strip of it. However, it looks like the installer didn't quite finish the job. I would probably do as you suggested and bury the edging deeper. You could also take up those few bricks that are outside the gate, level that area a little better and place those bricks closer to the edging for a more uniform look and to stabilize that immediate area.
Your particular brand, SnapEdge is simply too high.
You can find their various installation guides PDFs on the web-site.
But the clearest explanation comes from one of their drawings:
You need to remove the edge, and install it down below the gravel it's next to.
Or you can switch to another product where the edges to "under" the pavers; and are effectively hidden.
Can't upvote or comment at @alephzero's comment... but i'd say he's absolutely right: it was installed upside down. The part that is shown should be down in the dirt to keep a grip and not let the edging move with the seasons (frost heave or heavy rain runoff). The top surface won't be a collection of trip hazards as shown here.
Pull the spikes, turn it over, reinstall, and then finish by covering up the top layer with dirt or mulch or whatever matches.
I suspect some klutz nailed it down back to front, and the raised edge is meant to be on the opposite side, along the edge of the bricks outside your property. If that would make your gate shut properly, just turn it round.
A slightly raised edge may be intentional, since it will stop rainwater runoff flowing downhill and ending up where you don't want it.
The mentioned installation instructions say:
[...] our paver edgings may also be installed up against the paver, with the horizontal leg on the outside, if the installation requires it.