Contrary to what those who are against the correct translation are saying...
WITH YOUR SPIRIT is deep in history and meaning!
Let me share to you the reasons:
In the Bible, St. Paul, greets the early Christians this way:
"The grace of our Lord Jesus Christ be with your spirit, brethren. Amen." (Gal. 6:18)
"The Lord be with your spirit. Grace be with you." (2Tim. 4:22)
"The grace of the Lord Jesus Christ be with your spirit." (Phil. 4:23)
As this quotations say, the reply et cum spiritu tuo (“and with your spirit”) is an acknowledgement by the people of the grace and presence of Lord who is present and operative in the spirit or soul of the priest.
This was what St. John Chrysostom said when he gave his catechesis about the response "et cum spiritu tuo"
" If the Holy Spirit were not in our Bishop [referring to Bishop Flavian of Antioch] when he gave the peace to all shortly before ascending to his holy sanctuary, you would not have replied to him all together, And with your spirit. This is why you reply with this expression…reminding yourselves by this reply that he who is here does nothing of his own power, nor are the offered gifts the work of human nature, but is it the grace of the Spirit present and hovering over all things which prepared that mystic sacrifice."
St. John Chrysostom (Pentecost Homily)
When a man is ordained priest, the Holy Spirit comes to him and leaves that indelible mark in his soul. By responding "And with your spirit" and not just a mere "And also with you." we acknowledge that mark in the person most especially the soul of the priest.
So when you respond when the priest says "The Lord be with you." remember the deep history and meaning of that greeting.
It is not a simple "Good morning."
So to priests..........
STOP GREETING US GOOD MORNING FOR CRYING OUT LOUD!!!