The speaker begins by admitting he can't explain love. He claims the blind, the deaf and the mute all understand it better than he does, and he isn't sure whether what he feels is sorrow, joy or plain desire. Songs and books leave him cold, and the childish "Aay bee cee dee" suggests words alone have failed him.
Then he comes home tired, and a dog rushes out to greet him. The scene is messy and loud: licking, jumping, scratching, howling, a tugged shirt. Yet when the speaker kneels and hugs the dog, the animal goes still in his arms. That quiet moment is where the poem finds its answer. His heart feels like a full cup, and in the dog's eyes he sees his own face but doesn't recognise it, as if being loved shows him a new version of himself.
The mood moves from doubt and wry self-mockery to warmth and joy. The closing line, "your lesson in love," has a playful, showman's tone.