The mesh looks TERRIBLE, It contains so many unnecessary vertices, edges, faces. And the faces, NO.
And in the render, you turn the smooth shading on, but in your mesh, the edges, they are probably in flat shading. You don't even get enough bevel edge for the smooth shading, that's a reason for your bad rendering.
You may abused the Boolean tool and accidentally apply it to a high-res mesh. Or you just download, import the mesh from other file format.
There are two way to fix this mess:
- Join those unwanted topologies manually
- Remesh it by some tool and decimate to a reasonable resolution. (Instant Meshes might be a powerful one)
But the mesh it self isn't that complicated to craft, you might want (and need) to start it over again, with some good topologies.
Here is a good tutorial for this task: Blender Guru - Anvil