Two short lines, and almost everything in them is about a gap: the distance between what someone feels and what they can actually say. The speaker has "a thousand things" to tell another person, a number that suggests a flood of thoughts, feelings, or confessions built up inside. But the second line stops it cold. The words "won't come out."
What stands out is the phrasing. The speaker doesn't say they don't know what to say. They say the words won't come, as if the words have a will of their own, or as if something is blocking the way. The poem doesn't tell us what that something is. It could be shyness, fear of being rejected, or emotion so strong that speech feels too small. The poem leaves that open.
The mood is quiet, tense, and a little sad. There's longing in it, and frustration, but also tenderness: this is someone who clearly cares about the "you" they're addressing. The sudden brevity of the poem mirrors the problem. It begins to overflow and then simply cuts off, leaving silence where the thousand things should be.