During their rehearsal, Jennifer Nettles told John Glosson that she really wanted to "focus on his voice this week" (which we think is a good overall plan for any singing competition, really).

John chose 'How Great Thou Art,' the same tune he used when he auditioned for Jennifer, but he explained that singing it this week has special significance because it's the same week his mom found out she was pregnant with him. That may sound kind of oversharey, but then he said that the day after his parents learned they were expecting him, his 8-year-old brother died of leukemia.

He relayed the story to Jennifer, who, being human and not stone, teared up and said, "Even in the worst times, there is grace in sorrow." And this being 'Songs That Inspire' week, the song choice seemed especially fitting.

During his performance, he opened by doing the first verse a capella, which was just lovely, and then Jennifer joined him. They harmonize like they've been singing together for years, and overall it was gorgeous, powerful and heartfelt.

Afterward, Kelly Clarkson joked about having him kicked off surreptitiously because he's so good, Robin Thicke was thoroughly impressed, and John Legend said that although he's heard the song in church a ton of times, Glosson's version was stellar.

Watch Jennifer Nettles + John Glosson Perform 'How Great Thou Art' on 'Duets'