MS SQL Function to list roles

I need a simple function that will lookup an id and concatenate the values into a return string. I have a table that has a persons ID with a field that has a group of Program ID such as 1,2,3 or 4 or 1,4 and I need to lookup the id numbers in another table and produce the result of "Leader, Teacher, Researcher" or "Student". The values in the Program table will also a a sort order associated so they will not be in order based upon alph or insertions ID. Excel file is attached