The dispute that ran through Byzantine religious life for more than a century was about whether images of Christ and the saints could rightly be venerated, and it was argued at a high level on both sides. The case against rested on the commandment forbidding graven images, on the danger of confusing the representation with the one represented, and on the argument that Christ's divinity cannot be circumscribed, so that any depiction either divides the natures or confines the infinite.
The case for was worked out most fully by John of Damascus, writing under Muslim rule and beyond the reach of the emperor, and later by Theodore the Studite and the patriarch Nikephoros. Its core is the Incarnation: what has taken flesh has become depictable, and refusing to depict it implies discomfort with the flesh God assumed. The honour paid to an image passes to its prototype and does not stop at the material, so veneration of an icon is not worship of wood.
The argument produced a theology of the image that Orthodox Christianity has held ever since, in which the icon is not decoration or instruction but a form of presence, painted according to canons rather than invention, and the iconostasis and the veneration of icons in worship are not customs that could be dropped without changing the theology behind them.