Gods which shall go before us (theous hoi proporeusontai hēmōn). Exo 32:1. As guides and protectors, perhaps with some allusion to the pillar of fire and of cloud that had gone before them (Exo 13:21). The future indicative here with hoi (relative) expresses purpose.
Ye wot not (ouk oidamen). We do not know. How quickly they had forgotten both God and Moses while Moses was absent in the mount with God.
Become of him (egeneto autōi). Happened to him. “This” (houtos) here is a contemptuous allusion to Moses by the people.