HALOT page 757 says that
סלמ isn't a ladder. It's a stepped ramp, or a flight of steps. (It's a hapax, so this is based entirely on cognate languages.) In other words, well, a ziggurat.
I think (with emphasis on 'I') that the 'beholds' are simply descriptive of his dream experience. The dream presented itself to him as a series of reveals, one after the other.
It is thought that stepped pyramids have steps to emphasize their roles are connections between earth and heaven.
You asked, what would Jacob think? Well, you could mean, 'What would Jacob, as a typical ancient near-easterner think?' Or you might mean, 'What would Jacob, the patriarch, in particular, think?' I'll stick to the patriarch.
Now, here we go with my personal reading— when Jacob sees the angelic traffic, what he knows is that this is the real deal. The messengers going to and fro indicate that it is, indeed, the most high whom he is communicating with.
To look for a more specific function of the imagery, you might consider the circumstance that Jacob is on the, well, lam(b), far from home. The image of messengers coming and going might be suggestive of an eventual safe return. As well as emphasizing that his father's G-d is not purely a local deity, but is present, and active, over a wide range, including his (Jacob's) wanderings.
In the end, far be it from me to presume to give you a better answer than verse 16, which tells you exactly what he thought upon waking. We should all be so lucky as to realize that this about wherever we find ourselves.