The phrase "important prerequisite" means something that is necessary or required before something else can happen or be done successfully. It is like a step that must be completed before moving forward with something. Full definition
Long term and stable policy is the most important prerequisite for more sustainable energy. (windeurope.org)
Some students struggle in algebra because they lack important prerequisite skills, including facility with and understanding of fractions and fluency with basic number operations. (gse.harvard.edu)
The Confucian philosophy of learning and achievement places primary emphasis on nonintelligence factors — such as personality traits (e.g., motivation, perseverance, effort) and environmental factors (e.g., parental and familial support, teacher and school instruction)-- rather than natural ability as the most important prerequisites for desired performance (Chen & Stevenson, 1995; Rosenthal & Feldman, 1991; Shi & Zha, 2000). (ascd.org)