。
Studying requires great perseverance.
Literal
Study time [topic-は] great [na-な] perseverance [obj-を] need.
必要とする ('to need, require') is the formal/written equivalent of 必要だ — its verbal form, used when a subject 'actively needs' something. 忍耐 ('patience, perseverance, endurance') is a formal noun for the virtue of bearing hardship without giving up. 大変な as a な-adjective here means 'considerable, great' — not the adverbial '大変' ('very').