Rigpa is not something that you can extend. It is something that you have to develop a habit of, you have to train in it. In fact, what you are training in is the removal of the obscurations in order to be able to see the rigpa which is always there. There are two methods of doing this. One method is to get involved in creating virtue and to set about accumulating a lot of merit. The other method is to look directly at rigpa. To make an example for this: I have paper and I need to cut it. To cut it I need to have a knife and then to actually cut it. Accumulating merit is like making the knife.
Continuing to accumulate merit is like continuing to improve the knife, but not using it to cut the paper. Using rigpa practice is like actually cutting the paper. As far as these two methods are concerned, you could put a lot of effort into creating or furthering the tool that you already have by working on the accumulation of merit, but in the end you have to do the practice of rigpa which is the actual cutting.
Fearless Simplicity, p. 230