Worksheet Change Macro Runs Differently

When I step through a macro (sessions) or run the macro seperately, it works as intended. When I have it run off of a worksheet_change it doesn't work. Is there an easy fix for this?

Original

Sub sessions()
Dim a As Integer
Dim x As Long
x = Sheets(1).Range("a" & Rows.Count).End(xlUp).Row

Sheets(1).Unprotect Password:="password"

For a = 2 To x

If Cells(a, "m") = Cells(a, "d") And Cells(a, "m") 0 Then
Cells(a, "f").Resize(1, 6).Select
Selection.Locked = True
ElseIf Cells(a, "m") Cells(a, "d") Then
Cells(a, "f").Resize(1, 6).Select
Selection.Locked = False

End If

Next a