Get the free WordService collection of Services from the OS X App Store. Many of us use it. As part of its download, it installs services that provide shortcuts within Pages, and other applications. Select text to alphabetize in Pages, click the Pages menu > Services > WordService:Sort Ascending. In a second, your selected text is sorted in-place. Another service is capitalize intial word of sentences. Also very handy.
Once these services are installed, they are still not active for use in Pages, etc. Click the gear icon in your Dock to access System Preferences. Select the Keyboard preference panel, and the following in order: Shortcuts > Services. Scroll down in the right Services window until you see the WordService:Sort Lines Ascending. Check it to enable. Quit System Preferences. This sorting service is now available to you in Pages, TextEdit, Mail, etc.
If you click the Launchpad (rocket icon) in the left side of your Dock, you will find the WordService application icon. Click that, and then click its Help button. This will launch a PDF in Preview that lists all of the services and a brief description of each.