Look at that sea, girls--all silver and shadow and vision of things not seen. We couldn't enjoy its loveliness any more if we had millions of dollars and ropes of diamonds.

The speaker contrasts material wealth with the immediate, freely available richness of aesthetic experience. The sea—described in luminous, almost mystical terms (“silver and shadow and vision of things not seen”)—becomes a symbol of beauty that exceeds ownership and cannot be intensified by money. The line also reflects a recurring Montgomery theme: the moral and emotional education of learning to see, savor, and imaginatively inhabit the world. It suggests that true enjoyment depends less on circumstances than on perception, companionship, and a cultivated capacity for wonder—an implicit critique of equating happiness with luxury.