“Sitting With Me”, a lovely lilting number from Mary Mary’s sixth album Something Big, portrays the R&B duo as total Christian schooldorks. Mean kids call them “holy roller”, “Jesus freak”, and “geek”; they’re picked last for the team; they’re basically Taylor Swift in the “You Belong to Me” video. Like plenty of schooldorks, Mary Mary console themselves by remembering that Jesus was also unpopular—the last week of his life, anyway—and drive the point home by singing powerfully, “I’ll sit on the sidelines as long as he’s sitting with me!” Christian rocker Steve Taylor once memorably sang “Jesus is for losers”, and Mary Mary would surely agree.

But in the album’s best stomper “Something Bigger”, they hilariously sing, “Nobody plans to be a loser!” “Something Bigger”, like the rest of the album, is all about doing “great things ‘cause of God in me”. Mary Mary are determined to survive; they’ll never raise their white flag; when they see the haters standing around, they get ready for war. The album even opens with a quasi-military call-and-response cadence. Erica and Tina, the two beautiful and non-dorky sisters who make up Mary Mary, clearly have no desire to hang around in Loserville.

So they’re content on the sidelines with Jesus, but Jesus is also urging them to get in the game. (Or, you know, the war.) This isn’t a contradiction, exactly; the key, the escape hatch, is that phrase “‘cause of God in me”. Through God, say Erica and Tina, even losers can do great things. But when it comes to describing those great things, they’re frustratingly vague. “Better get your mind right”, they advise a dreamer who’s leaving the ghetto for the good life, but they never specify what a right mind or a good life look like. Since this is a gospel album, you can bet rightness and goodness have something to do with God, but God’s an easy answer. In Mary Mary’s lyrics, God is the mortar that pastes over any uncertainty, the bromide that soothes any unease.

The duo have a much clearer idea of what greatness sounds like: current mainstream R&B. Sonically, they’re in the game. These songs cover a lot of ground and they spare no expense. This is thanks to Mary Mary the songwriters, and also to Erica’s husband, producer Warryn Campbell (he helmed Kanye West’s “Homecoming”, among many other songs). Campbell and his team can churn out huge futuristic marches (“Something Bigger”, “Blind”), smooth keyboard-driven grooves (hit single “Walking”), warm acoustic ballads (“Homecoming Glory”), and songs that sound scarily like that Train song with the ukelele (“Are You Ready”). Occasionally they’ll manipulate the sisters’ voices or throw in some nifty electronic segueways, but nothing too outlandish. Their kick drum sounds are things of wonder.

Also wonderful are Erica and Tina’s voices. The sisters sing clearly and richly, moving from solo lines to well-arranged harmonies. Every note seems perfectly calculated to deliver as much pleasure as possible. In fact, if there’s any fault in the music on this album, it’s that vocals and production seem overly-planned and non-outlandish throughout. Mary Mary do some melismatic improvising when the songs call for it, but they never oversing. A couple boring tunes aside, the music is hard to fault, but it also rarely surprises.

Something Big is a solid Christian R&B album, but it’s frustrating. It hints at an audacity that its lyrics and music never quite deliver. Shortly after the aforementioned line about losers, Mary Mary sing, “Why stop at the ceiling when God showed me the sky?” Next time out, they should take their own advice.

• Multiple songs MySpace