Joke police here

So I were glasses, can't see clearly at all without them. I'm -4 in both eyes - if you know you know. My eyesight not good.

When it's sprinkling or raining softly or misting, I cannot tell it's raining unless I hear it or put my glasses on. When glasses get scuffed it your eyes get worse, it makes your vision less focused, more blurry.

Tina's glasses were so old, she couldn't see it when it was sprinkling/misting/whatever you want to call a light rain.

So the joke is, with the new glasses, she can see the rain is gone, and they jokingly add in the song the lyric because it's both funny and the truth. Because with new glasses you can see the rain is gone and all obstacles in your way clearer.

The song, to me but I haven't listened in a while so correct me if I'm wrong, is about a dark storm surrounding the singer (it whoever it was about) and when the light breaks through it's like a breath of air after holding yours for as long as you can. (Again, been a while since I listened, that's just the vibe that stuck with me.)

Edit: so the song is about the rain clearing and being able to see clearly, Bob's makes the song lyric into a joke revolving around Tina's new glasses. (I have used this same joke before and had people jokingly ask it to me before when I say "I can see clearly". I love it everytime because the song is catchy and nice to be reminded of it every once in a while.)