In a comment below, Peter mentions Raphael's "Disputation on the Sacrament."
Fr. Timothy Verdon is working on a book on St. Peter's Basilica; an excerpt, on Raphael's painting, is found here.
For the sensibility of that time, the immediate impact, the primary message of the fresco, was of an eschatological character. It clearly showed the relationship between the Church militant upon the earth and the Church triumphant in heaven.
And then, in the apparent confusion of the scene, beyond the strange platform of clouds that divides the wall horizontally, the viewer would have noted the vertical axis defined by: God the Father above; Christ, who is displaying his wounds, in the middle; the Holy Spirit in the form of a dove descending in a nimbus of glory below Christ; and further below – on the altar placed upon three steps at floor level – the Eucharistic host in a monstrance.
So after the first impression, which would have been generally eschatological, or referring to the end times, the attentive observer would have made more specifically theological, even dogmatic, reflections: a central trinitarian structure and the sacrament as the visible extension of the life of the three divine persons, the object of attention for the figures gathered around the altar at the bottom.