when we say to the celebrant of the mass, the lord be with your spirit doesnt it imply that we dont want the lord to be with his body also? doesnt it leave the celebrants body vulnerable to the attacks of the evil one?
No, that is not the meaning of the words “and with your spirit.” Remember, the priest begins by saying “the Lord be with you.” The priest is recognizing that the gathered assembly is the Body of Christ and is present in a special way. The congregation responds by saying “and with your spirit” because Christ is present in the priest or bishop in a special manner that is distinct from Christ’s presence in the gathered assembly. By virtue of ordination the priest and bishop have received an indelible mark upon their soul. They are configured to Christ in a special way that is not part of the laity.
As St. John Chrysostom wrote in his Pentecost Homily:
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.