Primary muscles used for serving

[vin]

There has been a lot of recent talk about what muscles to keep loose and what muscles to actually contract to develop a smooth and powerful serve, but there are a few parts that confuse me.

Starting from the beginning to make sure I have it right ...

The arm all the way to the hand should be loose throughout the motion, but it's hard to keep a loose shoulder since it's helping to lift up the arm and keep the elbow elevated.

It's important to stretch the shoulder/chest and retract the shoulder blade to provide a stable position with no slack so it can be efficiently brought into motion through abdominal contraction and shoulder rotation.

Where I start to get lost (if I am even correct to this point) is when I hear about using the chest and lats in the serve. If someone could elaborate on this, I would appreciate it.

I can see using the lat muscle to pull the shoulder down in addition to pulling it back, but why would this be beneficial? More shoulder stability? More conducive to an upward swing?

As for the chest, I don't even have an idea on how it's used.

Thanks,
Vin