Man has devised thousands of religions throughout history, and just as when he has made graven images and idols to worship, he has chosen to worship a god of his own making. He has reversed the process, and instead of man being created in God's image and likeness, he has imagined a god in his likeness. The Apostle Paul wrote:
"Professing themselves to be wise, they became fools, and changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things. Wherefore God also gave them up to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves: Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen" (Rom. 1:22-25).
So, in other words, righteousness comes from worshiping the real God, the only God, Whom the New Testament reveals is manifested in three Persons (Matt. 3:16-17; 28:19; Jn. 14:16, 26; Acts 2:33; Rom. 15:16; 2 Cor. 13:14; Eph. 4:4-6; etc.). When Abraham believed God, He was not aware that God was a Trinity, because that revelation came with the Advent of Jesus Christ.
But what about those religions that believe in the God of Abraham, Isaac, and Jacob? Does that mean those folks are saved? Not necessarily. For it is one thing to believe that God exists, and quite a different thing to believe what He says. Abraham didn't just believe God exists, he believed what God said. I would remind you that the Jews and Satan's fallen angels believe He exists. But the difference is, they do not believe in Him; they do not believe His Word. I am from Missouri, and like James, I will believe you believe when I see your fruit; he wrote:
"Even so faith, if it hath not works, is dead, being alone. Yea, a man may say, Thou hast faith, and I have works: shew me thy faith without thy works, and I will shew thee my faith by my works. Thou believest that there is one God; thou doest well: the devils also believe, and tremble. But wilt thou know, O vain man, that faith without works is dead?" (Jam. 2:17-20).