The speaker again describes both paths positively, saying that both were unsoiled (not “trodden black”) by footsteps.
What is stanza?
Because both were perhaps of equal value, he acknowledges that he thought it would be nice to come back to the first path at some time.
On the other hand, he realizes that, realistically speaking, he probably won’t have a chance to return to the first path. He says “way leads on to way,” meaning that choosing the one path will be followed by other choices and other paths, and he will never happen to come back this way to the first path.
In sum, the speaker mentions that he might regret picking just one of the paths, but he is also resigned about the choice. He could regret not picking that path, but he doesn’t really express regret.
Therefore, The speaker again describes both paths positively, saying that both were unsoiled (not “trodden black”) by footsteps.