will not be weighted down

Exo36 has the Israelites turning over vast amounts of their own resources for the building of the materials commanded by God. In fact, so much stuff Moses has to virtually throw out an edict to stop. That level of complete faith and proper response is the model for how we should respond to grace/mercy.

This occurs, however, directly after the whole calf incident, so there's no purity in the action here. I'm sure some of them were reacting out of guilt for their earlier participation; some were probably acting out of stark terror (what with the whole killing of the brothers thing after the calf); and some were acting out of a changed perspective.

I think it's easy to fall for the trap of trying to see how the good does or does not outweigh the bad, since the majority mentality is that sin is this zero-sum game, and that good works matter. Cancel that line of thought, sheep -- bad math.