Change Array to Variable for Email

Change Array to Variable for Email

This is the end results of print_r($modelfinal);
Array ( [0] => test [1] => test2 [2] => test2 [3] => test2 [4] => test2
[5] => test2 [6] => test2 )
However, I need to assign this to an email, and when I call the variable
it should print "test1, test2, test2,..." and so on. Right now, the email
only says "Array" when I call $modelfinal.
How do I do that?