And We haven’t sent any Messenger before you except that We revealed to him: "There is no deity except Me, so you serve Me alone".
Mankind created in Paradise is deputed to earth to be the vicegerent of the Impartial Lord. But when they started to deviate from Adhikr (the Straightpath), Lord sent down Adhikr through His 313 Messengers from Noah to Muhammad to remind mankind about the aim of life. After 30 years of Messenger’s departure, Islam has deteriorated and the Book reading people became into three groups: (1) The hypocrites, (2) Kuffar (3) Believers. Out of the three, the believer will only testify Adhikr and will inherit Paradise, whereas the Fujjar (hypocrites and Kuffar) who are hiding and rejecting Adhikr are the disbelievers destined into 7 doors of Hell as explained in verse 15: 44.
Today, Adhikr is codified as the Splendid Book. And as there is no group of believers anywhere in the world, the odd believer has to follow a lifestyle explained in verses 7: 205-206. See explanation 3: 7-10; 4: 150-151 and 15: 90-91.