The meaning of a poem is the experience the speaker (of the poem) or the author communicates. While, the idea is the underlying concept of the poem. Something which can be a generalization of live value. But, idea is not a message, since poems communicates experience more rather than gives moral message. I think the only way to understand meaning and idea is by asking two questions. For meaning,
what experience is the speaker telling about? --> e.g. A man walking in the wood and has to choose one of two roads (The Road not Taken)
What concept of life is implied in the poem? --> e.g. Man should always choose between two (any) choices in his life
The meaning of the poem is the experience it expresses, nothing less. Some of the readers are baffled by a particular poem and ask perplexedly: what does it mean? They want something they can grasp entirely with their minds. To tackle this problem, we distinguish the total meaning of a poem from its prose meaning. Total meaning the experience that a poem communicates and which can be communicated in no other way. Prose meaning the ingredients that can be separated out in the form of a prose paraphrase a prose meaning may be an idea. It may be a story, a description, a statement of emotion, a presentation of human character, or some combination of these. Some poems may not be directly concerned with ideas. Such poetry baffles the message hunters. Yet ideas are also part of human experience, and therefore many poems are concerned, at a part of the total experience that it communicates, the value and worth of the poem are determined by the value of the total experience, not by the truth or nobility of the idea itself. This is not to say that the truth of the idea is unimportant, or that its validity should not bee examined and appraised but a good idea will not make a good poem, similarly an idea not liked by the reader will ruin a poem. Good readers of poetry are receptive of all kinds of experience, poetry readers should be selling to entertain imaginatively, for the times bring, ideas they objectively regard as untrue. It is one way of understanding these ideas better, and of enlarging the reader's own experience. The primary beliefs a poem depends not so much on the truth of the idea presented as on the power with which it is communicated, and on its being made a convincing part of a meaningful total experience. We must feel that the idea has been truly and deeply felt by the poet, and that is the doing something more than mere moralizing.