There are a lot of different religions in the world, but three of the major religions that people follow are Christianity, Islam and Judaism. The cool thing about these religions is that they all have sources in Israel, a land that has created the world as we know it today and has played an important role in the founding of the three major monotheistic religions of the world. This is one of the many reasons why Israel has become an important global site. Not only is the location much more suited to religious experiences, but it provides lots of artifacts and buildings that are sacred to these religions.
Jerusalem is one of the oldest cities in the world and it has a highly diverse range of religions being practiced in it. You can see ancient mosques and even older synagogues, and the churches in this as well as a number of other cities will be wondrous to behold. The architecture has been modernized in some instances, but if you do some searching you will definitely find more places that are going to be worth your while. These buildings will be more in the older style, so if you are into ancient architecture you will be able to get a glimpse of the way people did things hundreds or even thousands of years ago.
There are a few things that you need to do in order to prepare for Israel as well. You should learn a bit of Hebrew so that you can talk to the local populace, although most people that you will meet in urban centers will be quite fluent in English. You also need to read up on Israel water quality so that you can avoid getting sick on your journey.