Summary: "I figure I have a better chance of running into Jesus here than most places."
"The Lord be with you;" "And with your spirit." The roots of this dialogue is based on when God shared Moses' spirit with the 70 Hebrew elders in the Book of Numbers, verse 11:25. The verse says that God took some of the spirit that was upon Moses and put it upon the seventy elders; and when the spirit rested upon them, they prophesied.
"And with your spirit" is a statement of right relationship because the "spirit" referred to is the priestly character or seal of the ordained minister. The Catechism explains that the seal is an indelible 'character' imprinted by the three unrepeatable sacraments of baptism, confirmation, and holy orders. (cf. 2 Corinthians 1:22; Ephesians 1:23, 4:30).
When the priest says, "Pray that my sacrifice and yours..." This emphasizes that the priest is standing in the person of Christ, essentially offering the same sacrifice that Christ offered on Holy Thursday and Good Friday. It also emphasized that the people are offering their own sacrifice- their very lives--that are joined together with the offering of bread wine.
A dying church is more concerned about social change than they are about seeing people changed by the power of God. Saint Mother Teresa and her sisters worshipped at Mass every morning at 4:30am. Mother Teresa knew how crucial this was. Seeing Christ in the Eucharist enabled her to see him in the streets. “If we recognize [Jesus] under the appearance of bread,” she explained, “we will have no difficulty recognizing him in the disguise of the suffering poor.” This is why Mother Teresa could say, “I have an opportunity to be with Jesus 24 hours a day.”
E.g. A successful person in his profession volunteered at a clinic that cleaned the feet of homeless people at a foot clinic. He would sit on a stool before a homeless guest, take the guest's feet and place them in a basin of warm water. After washing them, he took a towel and dried the feet, applying ointment to their sores. When asked why he did this, the man answered, "I figure I have a better chance of running into Jesus here than most places." That's a pretty good explanation