The religious population reproduces much more quickly than the secular population and have more children. If you look at the 2 extremes of the spectrum, the orthodox women will marry at around 21 years old and have 6-10 children. The secular women will marry (or not) at around 28 and have 2-3 children.
Republican former Virginia Governor Jim Gilmore files paperwork to enter presidential race (AP)
from the article: Poll: Fewer than half of Israelis see themselves as secular