If cell contains text string then run macro, otherwise stop macro and popup message

Try this...

Sub CheckAndContinue()

If InStr(1, Range("I2").Value, "Net", vbTextCompare) = 0 Then
    MsgBox "Condiotion does not match in I2 Cell", vbInformation, "Invalid Text"
    Exit Sub
End If

'Your Code Goes Here.....

End Sub