"I love thee to the depth and breadth and height my soul can reach, when feeling out of sight for the ends of being and ideal grace"- I believe she is saying that she loves him to beyond her soul, beyond her very being that she cannot herself comprehend just how much she loves him.
" i love thee to the level of every day's most quiet need, by sun and candlelight." Perhaps she is saying he is a quiet man, and though he does not speak much she still needs him there, we do not take particular notice of the sun, but if it were gone we would surely notice. "I love thee freely, as men strive for right." her love is equal to the eternal fight for right. "I love thee purely, as they turn from praise." She loves him purely, perhaps in the religious way, though others turn from praise, or maybe God, she will love him purely. " I love thee with the passion put on to use in my old griefs, and with my childhood's faith." she loves him just as strongly as her past griefs and she has the faith of a child in him, strong and unwavering. " I love thee with a love I seemed to lose with my lost saints." just as the saints have been lost so her love is lost in him. Even with all the pains in her life she has loved him and if God allows, she will love him still after death.