I started a vintners reserve cabernet sauvignon kit and the gravity before adding yeast was 1.040 instead of 1.070 that the instructions were saying. Is this a problem?
yes, because it will produce a wine w very very low alcohol...double check your readings...i would find your reading highly unusual from a kit manufacturer
IMO even 1.070 would be very light for a Cabernet Sauvignon. That would lead to something around 9% where most Cabernet Sauvignon are in the 12-13% range.