Liturgy Lines

The General Instruction of the Roman Missal has a chapter about the arrangement and ornamentation of churches for the celebration of the Eucharist. It begins by spelling out clearly the sacred nature and symbolic significance of the altar:

The altar is the table of the Lord to which the People of God is called together to participate in the Mass and the centre of the thanksgiving that is accomplished in the Eucharist. (296)
The altar signifies Christ Jesus, the Living Stone. (298)

Therefore:

Moderation should be observed in the decoration of the altar. Floral decorations should always be done with moderation and placed around the altar rather than on the altar table. (305)

Only what is required for the celebration may be placed on the altar table. (306)
Candles are to be appropriately placed either on or around the altar in a way suited to the design of the altar and the sanctuary and so as not to interfere with the faithful’s clear view of what takes place at the altar or what is placed on it. (307)

Floral arrangements, nativity scenes, flags, books and papers often clutter the altar area and distract from the ritual actions that occur there. Heavily coloured or decorated altar cloths, especially when draped to the floor, can detract from the dignity of the altar. Even candles are best placed beside the altar rather than on it.

The altar should be used only for the Liturgy of the Eucharist and never for preaching or making announcements. Readers and cantors show respect for the altar as the table of the Lord and a symbol of Christ by pausing and making a profound bow towards the altar when approaching the ambo.

Either on the altar or near it, there is to be a cross, with upon it the figure of Christ crucified, which is clearly visible to the assembled people. It is desirable that that such a cross should remain near the altar even outside of liturgical celebrations, so as to call to mind for the faithful the saving Passion of the Lord. (308)

The Introduction to the Lectionary for Mass explains that at Mass we are fed from two tables:

The Church is nourished spiritually at the table of God's word and at the table of the Eucharist:  from the one it grows in wisdom and from the other in holiness. (10)

So what is said about respecting the altar applies also to the ambo, the table of the word:

The dignity of the word of God requires that in the church there be a suitable place from which it may be proclaimed and toward which the attention of the faithful naturally turns during the Liturgy of the Word.
From the ambo only the readings, the Responsorial Psalm, and the Easter Proclamation (Exsultet) are to be proclaimed; likewise it may be used for giving the Homily and for announcing the intentions of the Universal Prayer (Prayer of the Faithful). The dignity of the ambo requires that only a minister of the word should stand at it.

As central liturgical symbols, the altar and ambo need to be noble and worthy pieces of art in their own right.