We ranging down this lower track,
The path we came by, thorn and flower,
Is shadow’d by the growing hour,
Lest life should fail in looking back.
So be it: there no shade can last
In that deep dawn behind the tomb,
But clear from marge to marge shall bloom
The eternal landscape of the past;
A lifelong tract of time reveal’d;
The fruitful hours of still increase;
Days order’d in a wealthy peace,
And those five years its richest field.
O Love, thy province were not large,
A bounded field, nor stretching far;
Look also, Love, a brooding star,
A rosy warmth from marge to marge.
I think the first stanza is saying that the shadow of forgetfulness of the past is a blessing in this life because the attraction of the past could quench the thirst for life in the present and future. Another interpretation is that the anguish we feel at past follies could extinguish all happiness in the present. My own experience is a mixture of both.
He is convinced that beyond death we shall be able to look back with complete clarity and joy seeing only the good of the past. He imagines Hallam is able to do this and that the five years of friendship with Tennyson will be for him “the richest field.” How easily Tennyson transfers his own emotion to his friend!
On the third line of the fourth stanza Tennyson himself commented, “as if Lord of the whole life”: the love shared by him and Hallam is only five years, ‘not large’ but because Love is divine, it is Lord of the whole life, it has no boundary. The image of a brooding star is interesting as we do not associate stars with a rosy warmth but with the cold of space or the fierce heat of their nuclear reactions. The image is odd, but I think it works.