Rain falls onto solid ground, and the poem stops to notice something simple: the ground is hard, yet the water still gets in. That small observation carries the whole piece. The speaker seems quietly struck by the fact that something so gentle can pass through something so tough.
The poem is short and plain, and the wording keeps it that way. "Hard" and "soft" are set against each other, and the second stanza spells out the surprise. Even the toughest surface, it suggests, isn't completely closed off. There's a hint that this might apply beyond rain and soil. Readers might think of a person who seems tough but can still be reached by kindness, or of how patience can wear down something stubborn.
The mood is calm and thoughtful, with a touch of wonder. Nothing is forced or dramatic. The speaker just watches, and finds a small kind of hope in what they see.