“The offering to the Lord from a sacrifice of well-being must be presented by him who offers his sacrifice of well-being to the Lord.”
The Hebrew word for an agent is shaliach. Betrothal may be arranged for an agent. If a husband gives a wife bill of divorce, he need not do it personally; he may entrust the bill of divorce to an agent. Likewise, the wife may entrust an agent to receive the bill of divorce.
The offerings for the terumah, the offerings set aside for the priests, a man could designate an agent to bring them. The Torah says that the whole congregation will kill the paschal lamb, but the whole congregation designates an agent to kill the paschal lamb.
In many situations a man (or a woman) designated (or designates) an agent, with only one exception: the person who brings the sacrifice of well-being is not allowed to designate an agent. Why is that?
I am puzzled by people who say, “Give regards from me to Person X.” Why don’t they tell him themself? Telephones are ubiquitous. The United States Postal Service reaches every corner in the Country. I have a Facebook account (I don’t go on Facebook; my account is dormant), but I want to see what an old friend is doing, I call him.
The well-being sacrifice is like that a person who’s calling a friend whom he did not see in a long time. Nobody can talk to that friend on behalf of that person. That’s why the person who brought the well-being sacrifice was prohibited to designate an agent.