Originally Answered: Christians - given the large number of Christian sects in the world ALL of whom claim to be the right one
You can know for yourself through revelation from God, which you can obtain by exercising faith and humbling yourself as a little child, and doubting not.
You are right. God, our Father in Heaven, is one God and there should be only one religion. Jesus Christ, our mediator with the Father, organized the Church as it ought to be but the people quickly began changing things.
According to the scriptures God's true Church would have prophets, apostles, bishops, elders, deacons, teachers, priests, patriarchs. The apostles would go from place to place as they did in the time of Christ, teaching, exhorting and correcting to keep all the congregations unified in doctrine and faith. The doctrine would be the same whether you attended one of their meetings in Polynesia or Spain, or any other place they are established. They would refer to one another as saints, brothers and sisters. It would be known as The Church of Jesus Christ, and He would be it's chief cornerstone.
He warned that He would not come again until there was first a falling away, so it would be a restored Church, because we are living in the last days and the signs that were foretold that would precede the coming of Christ are coming to pass, and heaven was to receive Christ until the times of restitution of all things, which God spoke of by the mouth of all his holy prophets since the world began.
They would tell of how Elias had come, how God had sent His messengers to restore long lost authority. They would preach repentance, baptism for the remission of sins, and the laying on of hands for the gift of the Holy Ghost.
They would have consecrated oil to heal the sick, raise up the dead and give sight to the blind in the name of Jesus Christ, and indeed have all of the gifts of the spirit.
They would have temples and know their purpose and understand the doctrine of baptism for the dead which Paul referred to in Corinthians. They would have the sealing power John spoke of in the book of Revelation. They would have the power to bind in heaven whatsoever they bind on earth. They would tell how Elijah had come and turned the hearts of the fathers to the children, and the hearts of the children to their fathers so the earth won't be smitten with a curse. They will know and understand why the woman cannot be without the man or the man without the woman in the Lord.
They would teach how another angel had flown in the midst of heaven having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue as John prophesied would happen in the last days.
They would strive for the perfection and unity that Christ commanded them to achieve, utilizing the holy Melchisedec priesthood, by which perfection comes. They would operate through the power of revelation. Their sons and daughters would prophesy, their old men would dream dreams, their young men would see visions. By their works, you will know them.
They would have missionaries that go out two by two into all the world. They would have the book spoken of by Isaiah that would whisper out of the dust, which was sealed, having a revelation of all things, which was taken to a learned man who said "I cannot read a sealed book" which was given to an unlearned man to read, who said, "I am unlearned" because the Lord said, Forasmuch as this people draw near me with their mouth, and with their lips do honour me, but have removed their heart far from me, and their fear toward me is taught by the precept of men, Therefore, behold, I would proceed to do a marvellous work among this people, even a marvellous work and a wonder: for the wisdom of their wise men shall perish, and the understanding of their prudent men shall be hid. They also that erred in spirit shall come to understanding, and they that murmured shall learn doctrine.
They would not preach for hire, that they may not be a burden to it's members, but teach every man to labor to support themselves and their families. They would teach thrift and industry, and extend their services and goods to help the poor and needy. They will not have a paid ministry, but do as Paul and Christ did, laboring for their own support that they might not be a burden to the people. They would devote the sacred tithes and offerings which the members consecrate without coercion, to the Lord for the building up of the Kingdom of God on the earth, for the preaching of the gospel. They would not forbid to marry or command to abstain from meat. Every gift and power that is spoken of in the New Testament would be incorporated therein. Satan would oppose the work with every ounce of energy he has at his command and with every soul he can enlist, so lies and deception lie in wait at every turn to keep mankind from partaking of the long awaited blessings which were promised by all of the holy prophets since the beginning.
It exists, God led me to it by revelation, and those who honestly seek truth will find it.