The size of Earth Wind & Fire’s ensemble, with two guitars, multiple drummer/percussionists, multiple vocalists, and horns, demanded a careful ear for arrangement (which is why so many of their imitators fell short of Earth Wind & Fire’s greatness).
What’s interesting to note here is that the primary puzzle pieces of the verse (the drums, the bass, and the guitarist strumming a repeating pattern in the right channel) also accommodate the second guitarist, in the left channel, who improvises a one-note accompaniment. This gives the piece more looseness, more of the spontaneous, improvised flavor of jazz. Amazingly, ample room remains for the vocals.
Such careful arranging is one of Earth Wind & Fire’s trademarks, and very difficult to pull off. Credit is due not only to the players but also to the judicious ears of their producer, the great Charles Stepney.