The time will come
when, with elation
you will greet yourself arriving
at your own door, in your own mirror
and each will smile at the other's welcome,
and say, sit here. Eat.
You will love again the stranger who was your self.
Give wine. Give bread. Give back your heart
to itself, to the stranger who has loved you
all your life, whom you ignored
for another, who knows you by heart.
These are biblical images that refer to Jesus' last supper.  Walcott makes “you” the Jesus figure. Therefore you should love yourself with the same intensity you might love Jesus and perhaps even implying that God is within us and to love yourself is part of loving God. 
 Note the three short, emphatic sentences beginning with ‘Give’, forming  syntactic parallels  that add to the impact.
Love After Love