Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Dim rng As Range
Set rng = Range("A1")

If Not Application.Intersect(rng, Range(Target.Address)) Is Nothing Then
        Call updateCells
End If
End Sub

Function updateCells()
Dim wb       As Workbook
Dim wsFirst  As Worksheet
Dim wsSecond As Worksheet

Set wb = ThisWorkbook
Set wsFirst = wb.Worksheets("Sheet1")
Set wsSecond = wb.Worksheets("Sheet2")

wsSecond.Rows(1).Insert shift:=xlShiftDown
wsSecond.Cells(1, 1) = wsFirst.Cells(1, 1).Value
End Function