Problem: You need to add some data about email recipient to message body, for example, his full name
Solution: Make use of $context.currentRecipientUser variable in your Message template. Here's an example:
<pre> Hi $context.currentRecipientUser.displayName, Issue <a href="$context.baseurl/browse/$issue.key">$issue.key - $issue.fields.summary</a> status was changed to $issue.fields.status.name by $context.currentUserDisplayName Best, Raley </pre>
Will render a greeting with the name of the Jira user who is receiving this email.
Check out Issue field picker → Recipient user for more fields that you can use right away in your Notification template.