"Like A Prayer" is very different from Madonna's previous music because of the gospel sound, so after the intro guitar lick (played by Prince), the song immediately attempts to establish this new territory. A door slams—it could be a church door—and cue the gospel choir. The gospel choir, which is joined by a church organ, sings the harmony, which is what the guitar would normally play through chords under Madonna's vocals.
The verse jumps straight into power pop, with the synth bass and drum part. The real fusion quality of the song comes in the second verse, where the gospel choir and organ rhythm section get a syncopated percussion companion. That fusion feel continues in the third verse where, upon the command "Let the choir sing," the gospel choir backs Madonna's chorus part. The song changes gears here, with the choir taking a larger role in the pop sections, adding clapping, and ad-lib response lines.
Ad-lib response lines are an important part of gospel music, and they are essentially melodic lines sung by vocalists in response to the lead vocal line. They are characterized by their emotionality, which comes in part from their improvised feel. Here the ad-lib lines come as the choir takes a larger part in the song, singing the line "Just like a prayer, I'll take you there" repeatedly, allowing one of the choir members to "solo" over the line. This adds to the authenticity of the gospel quality in the song. Madonna's commitment to the gospel sound makes its use in the song less a pop accessory and more an interesting musical tool that aided Madonna in establishing her credibility as a musical artist rather than a mere pop-culture "boy toy."