Student or Learner
How is "His land borders mine" different from "His land borders on mine"?
How is "His land borders the sea" different from "His land borders on the sea"?
"His land borders the sea" is not very good usage. "His land abuts, faces the sea" or even "his land is on the sea".
The words "limit" and "border" are very similar, but in practice (mathematics aside) a limit is the outer edge of something (and so "the sea limits his land"), while a border is the divide between two similar entities (so "his land borders on mine").
There is no difference in meaning between "borders" and "borders on" in this context, except that plain "borders" is briefer and likely more literary than "borders on", which sounds more natural in conversation.
The phrase "borders on", however, can also carry the meaning "verges on" or "approaches": Jim's advances to Mary border on the inappropriate.