Antiphons are passages (usually from Scripture) meant to be sung before and after verses from the Psalms or canticles of Scripture. An antiphon is a tool, citing a Scripture verse, to help the faithful to better understand the readings of a given liturgical day.
The Roman Missal (Lat. Missale Romanum) includes an Entrance Antiphon at the beginning of every Mass and also a Communion Antiphon. Those antiphons can either be sung or recited and also lengthened with psalm verses such as occurs with the Responsorial Psalm. Of those two antiphons, the Communion Antiphon is meant to foster a spirit of humility, adoration, and devotion as the people prepare to receive the Most Holy Body and Blood of Jesus.
When sung, music is considered to be sacred in nature to the extent that it more perfectly conforms to those realities. As the Second Vatican Council stated: “Sacred music is to be considered the more holy in proportion as it is more closely connected with the liturgical action whether it adds delight to prayer, fosters unity of minds, or confers greater solemnity upon the sacred rites.” (Sacrosanctum Concilium, n. 112). The antiphons fulfill this purpose because they are directly connected to explicit liturgical actions.
Each liturgical day is accompanied by antiphons that are proper to the particular celebration of the Mass on that specific day during a given liturgical season. Those antiphons have a unique power to foster certain attitudes and dispositions that are uniquely suited to worshiping the Lord during the Mass and they are even meant to be carried from the Mass into the worship that you offer in your daily lives – as the Latin proverb states: repetitio est mater studiorum (Eng. “repetition is the mother of all learning”). Ideally, as the antiphon is repeated, couched in that spirit of devoted prayer, the religious disposition the antiphon engenders will “settle into” the hearts and souls of those who recite or sing it, as long as the interior disposition it enshrines finds a heart open to its message.
According to the General Instruction of the Roman Missal, “During the priest’s reception of communion, the communion song is begun… If there is no singing, however, the Communion Antiphon found in the Missal may be recited either by the faithful, or by some of them, or by a lector. Otherwise the priest himself says it after he has received Communion and before he distributes Communion to the faithful” (GIRM, nn.86-87). The latter numbered section of the GIRM provides these four options: the official antiphon, a simple substitute for the same, an approved song, or something else suitable. The first option is the one that provides the clue to the ideal use: the preferred option is for the Communion antiphon to be taken from the Graduale Romanum (Roman Gradual) for sung Masses or from the Missal for spoken Masses.
Recommended text in regard to liturgical use of the antiphons see: Church Music Association of America. Communio: Communion Antiphons with Psalms, edited by Richard Rice.
Nature and dignity 