Answer:
1. Metaphor
2. The central message is that we should be compassionate and kind, not rigid, begrudging, or uncharitable.
Step-by-step explanation:
1. Metaphor refers to the comparison of things in an indirect form by stating that one thing is another. It resembles a Simile but the difference lies in the fact that Simile uses words like; as, and like to make its comparisons. When George MacDonald compares the heart to a casket, he applied Metaphor.
2. The central message of the poem borders on being largehearted, accomodating, compassionate, and kind. It encourages the reader not to have a rigid disposition but to be open and accomodating just like a wide-mouthed basket or a cup that overflows.