Neither with you only... but... also with him that is not here with us this day — i.e., “also with generations yet to be” (Rashi).
Related Commentaries of Deuteronomy 29:14
Deuteronomy 29:14-15
14 Neither with you only do I make this covenant and this oath;
15 But with him that standeth here with us this day before the LORD our God, and also with him that is not here with us this day: