Each of those little two-word phrases is part of the Order of Mass in Latin, each has been rendered in English in slightly longer phrases, respectively:
"The Lord be with you"
The word of the Lord"
"The gospel of the Lord"
"The Mystery of Faith"
"The body of Christ"
"The blood of Christ"
Each is an element of dialogue, each calls forth a response from those to whom it is directed. None of the phrases has a verb. This is not unusual in Latin; in the absence of a verb, one generally assumes a form of "esse" (to be) or "fieri" (to become). So we carefully add the verb "be" to "The Lord be with you," because it's ambiguous, but still allows conversation. "Be" is a subjunctive usage in English. It can mean "may the Lord be with you", or it can be a sort of softened imperative (as in a blessing, because not even a priest can tell God what to do!), or it can just mean "is", which is kind of an archaic usage, but we're in very traditional territory here.
Each of these little two-word phrases is a kind of invitation into dialogue. Yes, literally, in the sense that we respond to them, but because they happen in liturgy, they are an invitation into a dialogue of life. The phrases, with readings, gestures, sacramental signs, and people, float around in the space and invite us into the grand mystery of Christ, dead and risen, gone, and present.
Think about the times that the dialogue "Dominus vobiscum/Et cum spiritu tuo" is exchanged at mass. There is one at the beginning of mass (sometimes a longer exchange is used, like, "Grace and peace of God our Father...be with you," but these are all options), one before the gospel, one at the beginning of the Eucharistic prayer, another version of it (Pax vobiscum) right before the kiss of peace and communion, and one last one at the beginning of the dismissal rite. What does that mean?
The liturgy is reminding us that God is present—with us, yes—but in us. In us as assembly. In us gathered as we begin. In us as we hear the gospel proclaimed, alive in the Word and alive in us. In us as we say again the great prayer of thanksgiving to God, asking for the transforming power of the Spirit in our lives and in our world. In us as we offer shalom, the shalom of the Messiah, to one another, and share the food and drink that make us one. In us as we are sent into the world to live the mission of the Messiah. In short, in us as Christ, brothers and sisters of the Beloved Son, who have been given in baptism the Christic identity by the gift of the Holy Spirit.
We keep forgetting who we are, so we have to remind each other over and over again. "Dominus vobiscum," the priest says, "the Lord be with you as you gather, listen, give thanks, share, are sent." "Et cum spiritu tuo," we respond, "you too," we say, "you, who are our community person, marked with the spirit as ours in your ordination."
Are you beginning to see why it's so important that we not mess around with the words? "The Lord be with each and every one of you." That's a riff. "Vobiscum" means "you, all of you". the sense is of many-as-one, not many-as-individuals. We get to the latter by the former. Furthermore, it's just bad form to change ritual dialogue. It's saying, "It's OK for me to improvise my part, but you should just say what you're supposed to say." My experience is that it gets weirder and weirder until you wonder whether it's even possible to respond. "A selection from the gospel of Jesus Christ, written to us from Matthew." Huh? No it wasn't. But I digress.
As we come to those acclamatory dialogues before and after the readings and at the offering of the Eucharist, again, we are asked to respond to the mystery of faith. "The word of the Lord," we hear, and we're specifically not told, "This is the word of the Lord." Why? Because the latter is too narrow and descriptive. "This" reading is not "the word of the Lord" in the liturgical sense: God's word is living and active. God's word is Jesus Christ, alive in this room, alive in the saying and living of these words, and we are invited to renew our baptismal calling to be the Word of the Lord as we respond. "The body of Christ", "the blood of Christ," we are offered at communion. It's specifically not "This is the body..." or "this is the blood," again, because it's too narrow a focus to think that the liturgy is talking simply about the transformed bread and wine. The mystery into which we are invited is to be the body and blood of Christ, to participate in the Paschal Mystery, day in and day out, as we were made in our baptism.
Mysterium fidei in a revised translation of the Eucharistic prayer lost the pronouns and verbs ("Let us proclaim...") and was stripped down to a similar acclamatory invitation: "The mystery of faith!" proclaimed over the Eucharistic meal, as the Holy Spirit is called over the offering. The dying and rising of Jesus, made present in the sacred meal shared among the baptized, is the mystery of faith which we sing. I get enthusiastic about that.
Being invited to awaken to the wonder of who we are, the sons and daughters of God: presence, word, gospel peace, body, blood, mystery of faith. This is who we have been made by baptism: Christ! This is the calling we have received. I try to remind myself about that as I say those responses, hard as it is not to be distracted by the well-meaning improvisations of some presiders and the still-new awkward formality of "and with your spirit." The wonder of the mystery ought to be overwhelming. and invite me to surrender more completely. The Easter season, through the feast days at the beginning of summer Ordinary Time (Pentecost, Trinity, and the Body and Blood of the Lord) relentlessly invites us to believe that the risen Christ is with us, and to carry his shalom to the world. But every Sunday's liturgy reinforces that reality with two little words that we hear over and over in our own language, a little Easter and a little Pentecost, telling us that we belong to Christ and to one another, and inviting us into a way of life that will make the love of Christ clear to all. Deo gratias!
Two little words. Let's hear it for the economy of liturgical grace.