Here Jesus is questioned by the Sadducees as to whom a woman will be married to at the resurrection, if she was widowed by her previous husband - of course they go to the extreme and have her marry 7 guys!! Jesus knows they are asking this to disprove the possibility of our own resurrection from the dead, which the Sadducees didn't believe in, so not only does he tell them the question is stupid (there is no marriage after you are resurrected, maybe you are too busy getting to worship God up close and personal). He then goes on to answer their hidden question, which is does the resurrection exist, which He does by quoting God at the burning bush when He refers to Abraham Isaac and Jacob in the present tense. This quote unfortunately doesn't have as much impact in English as apparently it would have in Hebrew (otherwise Jesus wouldn't have used it).