How to programmatically select every nth row in a range in Excel

Sub SelectEveryNthRow()
    ' Initialize ColsSelection equal to the number of columns in the
    ' selection.
    ColsSelection = Selection.Columns.Count
    ' Initialize RowsSelection equal to the number of rows in your
    ' selection.
    RowsSelection = Selection.Rows.Count
    ' Initialize RowsBetween equal to three.
    RowsBetween = 3
    ' Initialize Diff equal to one row less than the first row number of
    ' the selection.
    Diff = Selection.Row - 1
    ' Resize the selection to be 1 column wide and the same number of
    ' rows long as the initial selection.
    Selection.Resize(RowsSelection, 1).Select
    ' Resize the selection to be every third row and the same number of
    ' columns wide as the original selection.
    Set FinalRange = Selection. _
       Offset(RowsBetween - 1, 0).Resize(1,ColsSelection)
    ' Loop through each cell in the selection.
    For Each xCell In Selection
        ' If the row number is a multiple of 3, then . . .
        If xCell.Row Mod RowsBetween = Diff Then
            ' ...reset FinalRange to include the union of the current
            ' FinalRange and the same number of columns.
            Set FinalRange = Application.Union _
                (FinalRange, xCell.Resize(1,ColsSelection))
        ' End check.
        End If
    ' Iterate loop.
    Next xCell
    ' Select the requested cells in the range.
    FinalRange.Select
End Sub