Every instrument performed by Paul. Why am I impressed by that? I can do that. Still, I'm impressed by that.
Probably I'm pre-disposed to awe by the stratospheric singing and the care in the melody at every turn. I'd bet.
It's quite a love song. Above all, Paul seemed to seek a partner with the talent of comforting. Or maybe he didn't seek that quality but was very glad to meet it as his band the Beatles imploded in the late '60s. This song is a thank you to his wife for helping him through that time.
Linda McCartney, a skilled photographer with a long list of credits and music business connections from before she ever knew Paul (including a deep friendship to Jimi Hendrix), seems to have taken the skills of perception and sympathy that made her a poet with a camera and rolled them into her relationships too.
We can help each other. We don't have to be islanded, empowered free agents of unstoppable individual momentum. Selfless concern will not always be exploited.
Sometimes you just give someone voice to sing back to you.