"before My presence": What is the intent of this? So that no pretext be given to Israel to say that idolatry was forbidden only to those who left Egypt — wherefore it is written "My presence," i.e., Just as I live and endure forever and ever, so, you and your children and your children's children may not serve idols — to the end of all the generations.
Without the Phrase Before My Presence, Israel Could Have Argued
Mekhilta Tractate Bachodesh 6:14