Although it is a popular contemporary belief to state that there are three Abrahamic faiths, in actuality, the Bible does not contain any instruction to enter into a religion called Judaism or Christianity. Noah عليه السلام, Abraham عليه السلام, Ishmael عليه السلام, Isaac عليه السلام and Jacob عليه السلام came before the words Judaism and Christianity even existed.
"Abraham was neither a Jew nor a Christian, but he was Haneefan Muslimaa [an upright monotheist who submitted himself to Allaah], and he was not of those who associated partners with Allaah in worship." (3:67)
For this reason, the One who sent Abraham عليه السلام as a prophet addressed those who would dispute this matter, saying:
"O People of the Scripture (Jews and Christians), why do you argue about Abraham while the Torah and the Gospel were not revealed until after him? Then will you not reason?" (3:65)
Consequently, there is no such thing as three Abrahamic faiths, as Abraham عليه السلام and his descendants only had one system of belief, which was the way of his Creator سبحانه و تعالى. All of the prophets عليهم الصلاة والسلام were commanded to submit to the One God سبحانه و تعالى worthy of all worship, and to follow His single way. In Arabic, this form of submission is called Islaam, a comprehensive word chosen by the Creator to allude to the act of submitting to Him and following His message.
"And who would be averse to the religion of Abraham except one who makes a fool of himself. And We had chosen him in this world, and indeed he, in the Hereafter, will be among the righteous. When his Lord said to him, 'Submit [Aslim],'[1] he said 'I have submitted [in Islaam] to the Lord of the worlds. And Abraham instructed his sons [to do the same] and [so did] Jacob, [saying], 'O my sons, indeed Allah has chosen for you this religion, so do not die except while you are Muslims (i.e. those who have submitted themselves to God).'" (2:130-132)
All of the prophets عليهم الصلاة والسلام taught the same message of submission to the One God سبحانه و تعالى. Not only was the essence of their call the same, many manners of worship were also very similar from one prophet to another. [2]
However, different laws were revealed to different prophets عليهم الصلاة والسلام, according to the wisdom of the Knower of all things سبحانه و تعالى. This unity of religion was only affected after later followers of the prophets عليهم الصلاة والسلام changed the messages they were given and separated into different religions and sects. This splitting caused each religion and sect to name itself with a new name, as well as to envy the other religions and sects that differed with them:
" Indeed, the religion in the sight of Allaah is Islaam (submission to Him). And those who were given the Scripture did not differ except after knowledge had come to them - out of jealous animosity between themselves. And whoever disbelieves in the verses of Allaah, then indeed, Allaah is swift in [taking] account." (3:19) [3]
Notes:
[1] Aslim is the command from the Arabic word aslama, and the word Islaam and Muslim all stem from this verb of submitting or surrendering oneself to God.
[2] For example, Muslims are commanded to make ablution (ceremonial washing) before they pray, just as the former nations were too. With time, these nations left the way of their messengers, and consequently, have lost this and other forms of worship:
"And he set the laver between the tent of the meeting and the altar, and put water in it for washing, with which Moses and Aaron and his sons washed their hands and their feet... as the Lord commanded Moses." (Exodus 40:30-31)
Muslims bow, kneel and prostrate in their prayer, just as the former prophets and their followers had:
"O come, let us worship and bow down: let us kneel before the Lord our maker." (Psalms 95:6)
"When Abraham was ninety-nine years old the Lord appeared to Abraham, and said to him, 'I am God-Almighty; walk before Me, and be blameless. And I will make My covenant between Me and you, and will multiply you exceedingly.' Then Abraham fell on his face." (Genesis 17:1-3)
"Then Jehoshaphat bowed his head with his face to the ground, and all Judah and the inhabitants of Jerusalem fell down before their Lord, worshiping their Lord." (2 Chronicles 20:18)
"And Joshua fell on his face to the earth, and did worship." (Joshua 5:14)
"...and they [Moses and Aaron] fell upon their faces: and the glory of the Lord appeared upon them." (Number 20:6)
Most present-day Jews and Christians find the act of prostrating to be foreign and even contemptible, even though the Prophets عليهم الصلاة والسلام and their true followers worshipped Allaah سبحانه و تعالى in this manner. However, for Muslims, prostrating before Allaah سبحانه و تعالى is the pinnacle of servitude to Him, because it shows that the Muslim has submitted him or herself completely to the Creator, which is the essence of Islaam. The New Testament states the Jesus عليه السلام prostrated and submitted himself to God: "And he went a little further and fell on his face and prayed." (Matthew 26:39)
[3] Haneef Oliver, Sacred Freedom: Western Liberalist Ideologies in the Light of Islam