The Start and Completion of the Way of Life of Islam (Submission to One God)
God started Islam (submission to one God) as the way of life for all of humanity when He made the monotheistic covenant with all humans, on the day of the covenant, via our spirits before creating us in body, mind and soul. We testified that He is our Lord, and we would worship Him to earn the afterlife. Later, God created Adam (peace be upon him) as the first human and His representative and told the angels to prostrate to him. All of them obeyed except Satan, who was of the jinn being. This is when the struggle of humanity of good vs evil began. God commanded Adam, his wife and their enemy, Satan, to go down to earth until the last day. He told Adam that He would send prophets and messengers (peace be upon them) with His guidance so his descendants could stay on the way of life or revert to it, if Satan had misled them. This process of steady guidance went on for thousands of years as humanity grew to face new challenges of their times.
God completed Islam (submission to one God) through His last and final prophet and messenger, Muhammad (peace be upon him), over 1400 years ago to tackle all the problems until the day of judgment. This is living the guidance in public and private at individual, family and community spheres as well as instituting Khilafah (representative governance) at societal and civilizational scales to lead the population. Humans chose free will so they could choose to believe in God and obey Him, or else follow Satan. If we believe in God and perform righteous and good deeds, we will earn the best of this world and the hereafter. However, if we engage in sinning, then we can always ask forgiveness and God will forgive but we must avoid major sinful deeds. If we follow Satan and continue to sin, he will mislead us into hellfire. This is the foremost struggle of defeating Satan and achieving the greatest triumph vs losing to him and falling into the mightiest catastrophe.