How to Speed up Excel VBA macro by adding two functions?

How to Speed up Excel VBA macro by adding two functions?

Sub normalspeed()

Dim StartTime As Double
Dim SecondsElapsed As Double

'Timer Begins
  StartTime = Timer

For i = 1 To 100
    For j = 1 To 100
        ThisWorkbook.Sheets(1).Cells(i, j).Select
        With Selection.Interior
        .Pattern = xlSolid
        .PatternColorIndex = xlAutomatic
        .ThemeColor = xlThemeColorDark1
        .TintAndShade = -4.99893185216834E-02
        .PatternTintAndShade = 0
        End With
    Next j
Next i

ThisWorkbook.Sheets(1).Range("A1").Select

'Time taken for code
SecondsElapsed = Round(Timer - StartTime, 2)

'Final Message
MsgBox "This code ran successfully in " & SecondsElapsed & " seconds", vbInformation

End Sub
Sub highspeed()
Call speedup
Dim StartTime As Double
Dim SecondsElapsed As Double

'Timer Begins
  StartTime = Timer

For i = 1 To 100
    For j = 1 To 100
        ThisWorkbook.Sheets(1).Cells(i, j).Select
        With Selection.Interior
        .Pattern = xlSolid
        .PatternColorIndex = xlAutomatic
        .ThemeColor = xlThemeColorDark1
        .TintAndShade = -4.99893185216834E-02
        .PatternTintAndShade = 0
        End With
    Next j
Next i

ThisWorkbook.Sheets(1).Range("A1").Select

'Time Taken for code
SecondsElapsed = Round(Timer - StartTime, 2)
Call speeddown

'Final message
MsgBox "This code ran successfully in " & SecondsElapsed & " seconds", vbInformation

End Sub

Function speedup()

Application.Calculation = xlCalculationManual

Application.ScreenUpdating = False

Application.DisplayStatusBar = False

Application.EnableEvents = False

End Function
Function speeddown()

Application.Calculation = xlCalculationAutomatic

Application.ScreenUpdating = True

Application.DisplayStatusBar = True

Application.EnableEvents = True

End Function