We have now begun the prayer, and thus we should lower our heads in reverence of Allah subhana wa ta’ala (glory be unto Him). When the Prophet ﷺ would pray, he would lower his head and keep his gaze on the ground towards the place where his head would fall in sujood, in humility to Allah (swt). Ibn Al-Qayyim said that a sign of a lover when he meets the beloved is he looks down, out of shyness and reverence- and this is exactly how we should be.