The themes are:
1. The sense-A lone traveller who has to ride long distances in order to fulfil what he has promised, finds himself by the woods late in the evening. But, the traveller much against his inclination to stay there for some time, moves on, as he has to cover long distances in order to keep his promise.
2. The feeling-One of nostalgia and a certain regret, as the poet feels that he would like to stop there a little longer and enjoy this beautiful sight , alone with nature.
3. The tone- Reflective---- the writer invites the reader to see the woods through his eyes.