Oh, and by the way, to give my “two-cent” answer to the TOPIC …
First are you asking because you want to know? Or have you already made up your mind and just want to announce to everyone else that you find it “silly,” not really interested in possibly learning something that, if believed, would radically change your life (if a person wants to be proven it, that's what it will do whether they accept it or deny it)? There isn’t a reason to give an answer to someone who just wants to debate. Debating declares a winner based on who gives the “best” answer, or who is the most talented speaker/writer.
To give a precise answer requires an apology, an ancient form of reasoning that comes to a conclusion based on the examination of evidence.
In debate people try to convince others of their belief or viewpoint.
In apology, the apologist attempts to show others that the reason for the Christian belief is sound. It is a defense of the reasonableness of a doctrine, but as a science it doesn’t attempt to convince or change the belief of the listener or audience. That action is called an “appeal.”
To attempt to answer with an apology: The whole thing is about declaring one’s belief in God as life giver via a ritualistic act.
If you believe in God the way the Jews, Muslims, and Christians do (not saying you should), then you acknowledge God as the source of life. Sacrifice is the ritual where one makes a public declaration to this belief and/or shows God that they believe this…. as a person who believes in his country may show this by sacrificing his time and life as a civilian to serve far from friends and family, even put his life on the line to demonstrate and defend his belief.
Because the JWs don’t believe in the Incarnation (the doctrine that one of the persons of the Trinity became a human being), the idea of Jesus giving his life on behalf of mankind does sound “silly,” as you put it. If you add the “missing ingredient” of the Trinity to the picture, then you will see what the majority of Christians are all worked up about, namely (won’t go into the Trinity here…good reason for other thread, but this is just to show how Witness view clouds the meaning of Christ’s sacrifice):
1. God wants to share his actual life, his divinity with human beings, not just keep them from dying. The Mosaic Law shows that people have to be practically God to live up to it and get life from its precepts, so God becomes human…God becomes like us so we don’t have to try to be like God through the Mosaic Law.
2. Since ritual sacrifice is an act of worship of humans to show their belief that God gives life, God Incarnate gives up his life to act in the opposite way of Adam. Adam committed not an act of sacrifice but an act of thievery with disregard to God being the source of life…in Christian theology this made death the lot Adam passed on to his descendants. Jesus sacrifice IS an act of sacrifice…and if the opposite act brought death, the reasoning is that the act of sacrifice brings life.
3. Sacrifice is antithetical in regards to life, so God uses a series of antithetical symbols and acts to show that he is the origin of life by producing life from symbols of “nothingness”: a woman gives birth to a child without being impregnated by a man, her poor son is actually the richest person in the universe, the Savior of the World is a laughingstock and is excommunicated by his own religion and executed as a criminal, the Tree of Life spoken about in Genesis turns out to be dead wood upon which this “Savior” is hung, this God of life dies, and Jesus is buried in a tomb carved out of the literal “stone the builders rejected," the rock believed unfit to construct the new temple of Herod and tossed aside (you can actually see it if you take the tour in Jerusalem). To prove God can do anything, even bring life from death or nothing (as well as to see if people will trust him by at least attempting to exercise faith in these things), God makes this life possible by destroying his own.
This is how their reasoning works. I am sure it leaves a lot of new questions (like Trinity, etc.) at bay…the point is that the whole sacrifice thing was one of the factors that lead to the Church’s belief in the divinity of Jesus, and this understanding lead to the sacrifice doctrine to make more sense.
Whether someone believes in it takes more than an explanation like this because belief requires more data with harder facts and their testing in order to go “out on a limb” and accept it. But this allows you to see the basic line of reasoning.