By Archbishop Michael Jackels
At the beginning of Mass, the priest greets the people by saying these or similar words: The Lord be with you, acknowledging the presence of Jesus when two or three people are gathered in his name.
The congregation responds: And with your spirit. This is not a reference to the Holy Spirit, but to the person of the priest, as if to say And with you too. So, the congregation acknowledges that Jesus is present with the priest as well.
Just like singing together at the beginning of Holy Mass, the greeting expresses that this is communitarian worship of believers, bound together by a common faith and purpose.
This greeting and response is repeated at other times: at the reading of the Gospel, at the beginning of the Eucharistic Prayer, and at the conclusion of Mass.