Classic Poem

Thou wear'st a padlock on thy heart,
A lock without a key;
And none shall force its clasp apart
Save only he
Who gets its mystic letters in a row,
And so
Is lord of thee!
What may they be?
Try these four letters, G, O, L and D!
It has not stirred.
Now try L, O, V, E — ah! that's the word!