The tone in the poem "The Secret Heart" is one of nostalgia, warmth, and love. The rhythm is set to the aa, bb, cc pattern. Metaphors are used to represent different things in the poem.
"His love had kindled in the dark" means that his presence in the room has demonstrated that he loves his son.
"too tender for the day to trace.” means that his father hides his love because he does not express it openly.
The whole poem represents something to the child different and yet the same as the father's intentions. The father enters the room to check on his son. His presence and concern for his son's safety and well being demonstrates his love. The boy sees something different that represents his father's love. He sees the light from the match enclosed in his father's hands in the shape of a heart. It is symbolic of his father's love.