To really get the most out of this title, you'd have to know a bit about an old guy named St. Augustine.
Never heard of him? Never fear. Shmoop's got the scoop. St. Augustine was a Christian thinker who wrote in the 4th century. Around 397 A.D., he wrote a little (okay, big) book called Confessions, in which he outlined his religious beliefs, with a healthy dose of autobiography mixed in.
If you read Confessions, in Book X, you'll stumble upon the following quote:
I have learnt to love you late, Beauty at once so ancient and new! I have learnt to love you late! You were within me, and I was in the world outside myself. I searched for you outside myself and, disfigured as I was, I fell upon the lovely things of your creation. You were with me, but I was not with you. The beautiful things of this world kept me far from you and yet, if they had not been in you, they would have no being at all. (source)
Yep, that's where Wilbur got his title from. Augustine's arguing that the things of this world kept him from communing with beauty and God because he was so busy looking outside, rather than in. Wilbur steals phrase (it's cool—writers do this all the time), and adds the "Love Calls Us" to elaborate on Augustine's point.
Only, there's no mention of love in the entire poem, so why include it in the title? The "things of this world" part we can understand—there is enough mention and observation about what goes on in the world's daily routine to fill the world's most boring diary. So the love part must be there in a subtler way.
What's love doing in the poem? It's calling us to the things of this world. And that makes sense, if you read the last stanza in light of the title. The soul is called back from its daydream to accept and love humankind and the flawed world. Sure, the soul could stay in its pre-dawn state, hanging out with the angels and living large. But every morning, it rejoins the body and all the messiness that comes with.
Why? Because it loves the body. It's love that returns us to ourselves every morning. It's love that gets us out of bed. In short, "Love Calls Us to the Things of This World."
Only, unlike for Augustine, for Wilbur, this is a very, very good thing.