The key assumption here is that a change in trend productivity growth affects wage change more slowly than price change - that is, productivity acceleration has an asymmetric effect on wages and prices. This is modeled by assuming that wage change depends on q*, while the inflation equation (based on the markup equation) depends on q.
Closer home, Kautilya, in his Arthashastra written in about 300 B.C., has also mentioned about the existence of powerful guilds of merchant bankers who received deposits, and advanced loans and issued hundis (letters of transfer).