This is something I've wanted to post for a while, and I'm finally getting around to it.
Yes, I could list you every talk that's been given on service and why we should all be serving. In fact, I've already given a lesson on service - the real reason we should serve - in the Parable of the First Responder.
Service can really help you when you are facing depression. President Hinckley continued a vigorous pace of service after Sister Hinckley passed away that is an example to us all.
There are a few cautionary things I would like to say regarding service.
If you are keeping yourself busy with service in order to delay the grieving process, don't. You need to take some time for yourself to go through the different stages of the grieving process. It doesn't mean you can't give service while this is going on, however when you're in the anger phase you might not want to be around anyone to keep from offending someone. If you know what I mean.
The other caution I have is this: make sure you do not run faster than you can walk. When Decker died, I threw myself into Family History. There was something I felt Decker and the Lord both wanted me to accomplish, something Decker was not able to accomplish before he died.
I accomplished a lot, in fact I don't feel the pressing need to work in that calling now as I did before, because of what I did accomplish, with the inspiration of the Lord. But I also found myself burned out by the time I was done with 7 Family History callings between the Ward and Stake levels. I listed them all on a document that I gave to both Ward and Stake Priesthood leaders and told each they would have to choose 1. I was released from the rest. Pretty soon, though, I was getting released from the two that they chose because I just couldn't do it anymore.
A lot of other things contributed to this, but I was very burned out and when that happens, you don't want to serve at all. That's why I have the caution to take things slowly and don't feel like people are going to judge you if you need a break. There are always the gossip mongers in each Ward, but this is between you, the Lord and your Bishop.