Many upper class, formal and technical English words are from Latin. These words are used in law, medicine, science and other high-status skills. For a long time the rulers of England were colonial Norman French. After some fighting*, English finally became the regular language of government, but the English people still needed to use some Latin/French words.
Important English words were borrowed from Latin when an English word was unavailable. During the Middle English period the functions of law and government were in the hands of Norman French kings. Of course they did not use English; that was the language of farmers. So even today words about government functions are from Latin. If you commit a crime, the government will send the police to arrest you and then a judge will tell you that what you did was illegal and send you to prison. All the key words in this sentence are from Latin, as follows (English/Latin): commit/committere, crime/crimen, government/gubernare, police/politia, arrest/arrestare, judge/iudex, illegal/illegalis, prison/prensionem. After the end of the Middle English period England kept the Latin (and French) words and made them into English.
Of course some of these words are from French. However the French language started as a dialect of Latin, pronunciation and spelling varied over time and eventually became a new language. For example (Modern English/Old French): commit/comitter, crime/crimne, government/governement, police/police, arrest/arester, judge/juge, illegal/illégal, prison/prison. The English word police came from the Old French word police, which came from the Latin word politia, which came from the Old Greek word polis (meaning city). We are often unsure if the English words were taken from French or directly from Latin (or even Greek).
In order to do the business of ruling themselves the English needed words for the functions of government. Those government words that they once had, had been forgotten over the centuries of Norman French rule. So they needed to keep some of the words of their former colonial rulers and we still use them today.
Footnote: In 1485, at the end of the War of the Roses, after the last Norman king was killed, Henry Tudor became Henry VII, King of England. With the start of the English Tudor dynasty, English was the language used by the rulers of England.