Refer to Excel cell in Table by header name and row number

A shorter answer is:

MsgBox [MyTable].Cells(2, [MyTable[MyColumn]].Column)

Much cleaner and easier!

In your example, something like this:

Dim tb As ListObject
'assumes Table is the first one on the ActiveSheet
Set tb = ActiveSheet.ListObjects(1)
MsgBox tb.DataBodyRange.Cells(2, tb.ListColumns("header4").Index)