Imaan (Faith) & Islam (Self-Submission)
Wholehearted submission to Allah's will
It is said in the Quran that the only religion in the sight of Allah ﷻ is Islam defined as "self-surrender" or "self-submission". As per Quran the purpose of humankind’s temporary existence on earth is to know the will of Allah ﷻ, which He revealed through His chosen ones called the Prophets and Messengers, and after knowing, submit to it willingly and wholeheartedly: (Al Quran 3:85) For, if one goes in search of a religion other than self-surrender (Islam) to God, it will never be accepted from him, and in the life to come he shall be among the lost. In Islam every word has a relation to its meaning and no word is meaningless. Islam means "self-submission" which is related to the word salaam which means "peace", and the term muslim means "the one who submits their will to Allah's will". The purpose of religion is to willingly submit to guidance delivered by Allah ﷻ, attain peace in this world and be successful in the hereafter, which is our destination. Hence the term Islam informs us about our purpose of religion and our existence on earth as opposed to terms like Judaism or Christianity or Buddhism or Hinduism.
For instance Judaism is a term referring to a set of teachings followed by the people who belonged to Kingdom of Judah. This term was coined by people and Israeli Prophets like Musa (Moses) (alaihi salaam) never referred to his teachings as such. Neither is the term Christianity coming from Isa ibn Maryam (Jesus son of Mary) (alaihim us salaam), a term coined by his followers quite a long while after him. Similarly, a citizen of land of Hind or “ancient India” is called a Hindu, hence Hinduism is a reference to the religious teachings followed by the people of that land. Therefore, it is quite easy to conclude that terms like Judaism or Buddhism (a term referred to teachings of a man named Buddha) are man-made, they are often found related to a land or a person, and their meaning is confined to the religious teachings of an ethnicity or a region. However, this is not the case in message of the Quran. Its message is universal and encompasses the entire humankind. The Quran reminds followers of previous prophets that their purpose was also to submit wholeheartedly to the teachings brought to them by those great prophets. But after those Prophets passed away, their followers changed their teachings due to mutual discords and formed in to numerous sects and coined new terms for their religion: (Al Quran 3:19) Behold, the only [true] religion in the sight of God is [man's] self-surrender to Him (Islam); and those who were given revelation aforetime took, out of mutual jealousy, to divergent views [on this point] only after knowledge had come to them. This resulted in them significantly losing the purpose of religion.
Thus it would be correct to say that since Islam is universally defined as “submitting one’s will to Allah’s will” then it is the only true religion and way of life in the sight of Allah ﷻ from the time of Adam (a.s) till now and will remain till the end of the world.
 Al Quran 3:85 – Asad Translation
 Al Quran 3:19 – Asad Translation