The book of Number counts the Israelites twice, two generations. The first generation count was 600,000. Because of their murmuring and complaining about God and their choice to continue sinning against God and not obeying Him. God passed judgement on the to wander in the desert for 4o years, until that generation passed. The second generation also had 600,000 people and it was this generation along with Joshua and Caleb from the first generation that was allowed to enter the promised land.