Simplified, the sentence reads:
Voces denotent eventum, ut id, quod propositum erat, vel absconditum sit, vel revelatum.
That is: "Words shall indicate the event, so that that which was proposed is hidden as well as revealed." (vel...vel can mean "X as well as Y," based on context I believe this is the case here).
Absconditum is explained thus: id est, non acceptum cum intellectu & sensu (that is, not understood with the intellect and sense)
Revelatum is explained as follows: id est, vera fide apprehensum (that is, grasped through true faith).
So all in all we end up with:
The words shall of course indicate the event by which it was done, so that the part of God's purpose which was put forth to be understood is at once concealed, that is, not understood with the intellect and the senses, and revealed, that is, grasped through true faith.
"The event by which it was done" is rather clunky, more context might allow for a better translation.