Bigotry tries to keep truth safe in its hand with a grip that kills it.
Tagore pictures truth as something alive, like a small bird or a flower. If you clutch it so hard that nothing can disturb it, you end up with something dead. Bigotry means well in its way. The bigot really does want to protect what he believes, but fear makes him squeeze, and the squeezing shuts out questions, other voices, and any chance that the belief might grow or be corrected. What remains is a slogan that looks like truth but no longer breathes.
This fits Tagore's wider outlook. He distrusted rigid dogma and narrow nationalism, and he kept returning to a humanism in which truth is larger than any one group, creed, or person. For him, truth is something you keep company with, not something you own. The line comes from his short aphoristic verses, which often work by a single quiet image.
Today, it might mean noticing what happens in you when a cherished conviction is challenged at a family dinner. If you feel your jaw tighten and start hunting for a winning reply, that is the grip. You could loosen it by asking the other person, "What led you to see it that way?" and actually listening. You may keep your view, but you will hold it more gently, and it will be healthier for it.