Passing Objects In

When you declare a variable with an Object data type it can assigned a value using the Set keyword.

Dim myObject As Object 
Set myObject = ThisWorkbook 

It is possible to pass an object into a subroutine or function

Call PassingIn(myObject) 

Public Sub PassingIn(ByRef myObject As Object) 
   Debug.Print TypeName(myObject) 
   'Workbook
End Sub 

Always By Reference

It doesn't matter if you pass in this variable using ByVal or ByRef, the object is always passed by reference.
This means that a reference pointer is passed in and not a copy of the actual object.

ByRef vs ByVal

There is a difference though between the following 2 lines
Public Sub PassingIn(ByRef myObject As Object)
Public Sub PassingIn(ByVal myObject As Object)
ByRef - Passes in the original reference pointer
ByVal - Passes in a copy of the reference pointer
The object will be modified in both cases
ByRef - Caller variable can be reassigned
ByVal - Caller variable cannot be reassigned

Example

Public Sub Testing() 
   Dim myObject As Object 
   Set myObject = Range("A1") 
   Call PassedByRef(myObject) 
   Debug.Print myObject.Address    '$B$1 - changed  
   myObject.Value = 20 

   Set myObject = Range("A1") 
   Call PassedByRef(myObject) 
   Debug.Print myObject.Address    '$A$1 - unchanged  
   myObject.Value = 20 
End Sub 

Public Sub PassedByRef(ByRef r As Range) 
   Set r = Range("B1") 
End Sub 

Public Sub PassedByVal(ByVal r As Range) 
   Set r = Range("C1") 
End Sub