If you are having a problem using Ableton Worship Strings Presets, you'll want to double check a few things.
First, make sure you've gone through the installation video and downloaded the free "Labs Strings" VST/AU plugin from Spitfire Audio here.
Then, make sure to go through all the steps in this video:
Spitfire recommend you have it here for Ableton to find it: Preferences > Plug-ins > Plug-In Sources
More troubleshooting Articles from Spitfire are here.
Learn more about saving your strings presets to use in any Ableton Live Set: