These lines are from Stopping by Woods on a Snowy Evening by Robert Frost written in 1922 (pub 1923) in his New Hampshire Vol.

The poem highlights the importance of enjoying the beauty and peace of nature while also fulfilling one's responsibilities and obligations, without becoming entirely lost in that joy.

The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep.