189 We desire to commend and urge the adornment of churches and altars. Let each one feel moved by the inspired word, "the zeal of thy house hath eaten me up"; and strive as much as in him lies that everything in the church, including vestments and liturgical furnishings, even though not rich nor lavish, be perfectly clean and appropriate, since all is consecrated to the Divine Majesty. If we have previously disapproved of the error of those who would wish to outlaw images from churches on the plea of reviving an ancient tradition, We now deem it Our duty to censure the inconsiderate zeal of those who propose for veneration in the Churches and on the altars, without any just reason, a multitude of sacred images and statues, and also those who display unauthorized relics, those who emphasize special and insignificant practices, neglecting essential and necessary things. They thus bring religion into derision and lessen the dignity of worship.
Source: Mediator Dei (Vatican.va)