These lines are from the poem "Sweetest Love, I Do Not Goe" by John Donne. In this poem, the speaker is reassuring his beloved that she should not be afraid of their temporary separation.
He draws a comparison between his journey and that of the sun. He argues that the sun ("He") departs every evening, yet it has no "desire" to return to a loved one, nor does it have the consciousness ("sense") to understand its journey. Furthermore, the sun's path is much longer ("Nor halfe so short a way" as the speaker's). Despite this, the sun reliably returns every morning. Therefore, the speaker tells his beloved, "Then feare not mee," because his own return is far more certain, as he has a powerful desire to come back to her and his journey is much shorter.