This is the opening line of 'The Shepherd' by William Blake (1757-1827), the innovative English poet, painter, printmaker and mystic.
The poem was first published in 1789 in Blake's well-known Songs of Innocence, and then republished in 1794 in the extended volume, Songs of Innocence and Experience.
How sweet is the Shepherd's sweet lot!/From the morn to the evening he strays,
He shall follow his sheep all the day,/And his tongue shall be filled with praise.
For he hears the lambs' innocent call,/And he hears the ewes' tender reply;
He is watchful while they are in peace/For they know when their Shepherd is nigh.
The words have been set to music on numerous occasions; one such setting is the "Pastoral - The Shepherd" by William Havergal Brian (1876-1972), published in 1922.