The newly-reunited couple appeared ''smitten'' with one another at the session at City Church in Los Angeles, where they sat quietly with friends and listened to a sermon from Pastor Judah Smith.
A source told Us Weekly: ''They were very lovey dovey and cute. They came and left together with a few friends
''They sat next to each other and listened to the sermon and were smitten with each other.''
And it seems the sessions have been having a positive effect on Justin, following months of controversial antics.
The source added: ''He looks so happy and at peace.''
The 20-year-old singer won back the 'Come and Get It' star - who he has had an on/off romance with since 2010 - after vowing to curb his wild ways and even change his friendship group.
A source told The Sun newspaper: ''He told her he can't live without her and that he's reformed his bad boy ways for good.
''He's ditched a few of the troublesome characters he's been hanging out with after advice from his management.
''And Selena thinks he's being genuine and given Justin another chance.
And as a symbol of his new direction, Justin presented Selena with a £6,000 Segway at his Beverly Hills home so they can have ''good, clean fun'' together.
The source added: ''It was when she agreed to go to his house that he gave her the new, shiny Segway.
''He thought a Segway would be a chance to prove they can have good, clean fun together, and she thought that was a really sweet touch.''
The singer introduced "the next generation" in Iceland.
Jack Antonoff hears a ''female voice'' in his head when he writes music.
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