Mail Merge is an AppleScript replacement for the mail merge feature that was omitted from Pages 5.
Create a Numbers document with one sheet, containing one table, with one header row and no header columns. Fill with data. Create a Pages document (if it has body text, almost certainly ending in a page break), and write "%Column Name%" to reference data in the column from your Numbers table whose first (header) cell is "Column Name". Open both documents. Run script. Rejoice!
What's new in Mail Merge
Fixed a bug that could cause first-time users to experience "System Events got an error: Can’t get button 4 of window 1 of process "Pages". Invalid index." number -1719 from button 4 of window 1 of process "Pages""