[To unite the entire empire, Emp. Constantine fused three (3) major religions in Rome to form the Roman Catholicism – Mithraism, Sol Invictus and Christianity.]
The premise of this statement suggests that the origin of Catholicism is not Jesus Christ but rather the outcome of uniting three different religions and Catholicism is distinct from Christianity. Such a claim is not historically accurate, it fact it exposes the gross ignorance and lack of scholarship by the person who uttered this statement. It is impossible that Catholicism is an outcome of uniting three religions because 1. Catholicism and Christianity are one and the same, and 2. Catholicism already exists even before Constantine was born. John Schwarz a Protestant authors admits that Catholicism can trace its origin into the time of St. Peter and Paul;
The Church in Rome [Catholic Church] was by far the most important church in Christendom: it was situated in the ancient imperial capital of the empire; it had the largest congregation of Christians; and its roots went back to Peter and Paul, the two greatest saints of the Church.
Common sense tells us that since the roots of Catholicism can be traced back into the time of St. Peter and Paul then the premise that Catholicism is a fusion of three distinct religions is wrong. How can Catholicism be a product of uniting three different religions if it already exists prior to the allege unification of Constantine? The statement also draws a distinction between Christianity and Catholicism, such a distinction do not exists because Christianity is Catholicism and Catholicism is Christianity, Roman Catholicism traces its history to Jesus Christ. The cause of dichotomy between Catholicism and Christianity is a lack of scholarship and knowledge of history akin to all those who opposes Catholicism.
[321 AD: Emp. Constantine declared (1) Sunday, “the day of the Sun” as the day of worship, and (2) moved the birthday of Jesus Christ from January 6 to December 25, the “Natalis Invictus” on Winter Solstice.]
This is another ploy to convince the readers to believe that Constantine has an internal contribution in shaping Catholicism. In fact Constantine’s only contribution to Catholicism is the Edict of Milan which gave Christians a freedom to exercise their belief in public, made Christianity the state religion. However, Constantine made no contribution in its doctrine and practices. Sunday as the day of worship was universally accepted by Christians even before the birth of Constantine. Philip Schaff a noted historian wrote;
“Sunday… was adopted by the early Christians as a day of worship… Sunday was emphatically the weekly feast of the resurrection of Christ, as the Jewish Sabbath was the feast of creation. It was called the Lords day, and upon it the primitive church assembled to break bread. No regulations for its observance are laid down in the New Testament nor, indeed, [sic.] its observance even enjoined. Yet Christian feeling led to the universal adoption of the day, in imitation of the apostolic precedence. In the second century its observance was universal.” Encyclopedia of religious knowledge 1891 Ed., vol.4, Schaff- Herzog
It is a baseless claim that it was Constantine who declared Sunday as the day of worship, how can he make such a declaration when Sunday was already universally accepted by Christians as the day of worship centuries prior to his allege declaration? Admittedly there is scarcity of information on how the Birth of Christ fall on December 25 there are a lot of theories surrounding this date, but one this is for sure Constantine has nothing to do with it. Biblical scholar Andrew McGowan stated that “The December 25 feast seems to have existed before 312—before Constantine and his conversion, at least.”
The earliest record of mentioning Christ’s birth on December 25 is on a fourth century Roman almanac that lists the death dates of various Christian bishops and martyrs. The first date listed, December 25, is marked: natus Christus in Betleem Judeae: “Christ was born in Bethlehem of Judea.” A close analysis of historical data will mostly debunk the accusations made by those who opposed the Catholic Church, they do not mind at all digging up the truth for them as long as it will put the Catholic Church in bad faith they will not hesitate to hurl it against the Catholic Church.
[325 AD: Emp Constantine convened the Council of Nicea Four (4) highlights: 1. Easter Sunday was established at the onset of spring 2. redefined the authority of the church, thus given more power 3. established the “Holy Trinity” as three (3) persons in one (1) god, and 4. voted Jesus Christ as god – an apotheosis.]
This is another attempt to discredit the Catholic Church by making the readers think that Constantine was responsible for the decrees and teachings of the Council of Nicea. But first we have to have a brief background about the Council and what is Constantine’s contribution in this great council of the Church. The council was convened due to the confusion that swept through the entire Christendom, a man named Arius started to teach that Jesus Christ is not God and his heretical teaching is spreading like a wild fire. So a council was necessary to settle the dispute and defend the orthodox Christian faith the Jesus Christ is fully God and fully man.
The Council was attended by bishops from all over the world and since the pope was already old and ailing he sent a priest to represent him in the council. Against Arius it was St. Athanasius who defended the orthodoxy of the Christian faith arguing from the Scripture and history that Jesus Christ is God. So, what is the role of Constantine in this council? According to a Christian historial P.C Thomas he wrote that;
for the first few centuries the emperors played a prominent part in summoning and conducting the Councils. In those early years the bishops were poor and they needed the support of the emperor for their transportation and lodging. Furthermore, the emperor considered themselves protectors of the Church and took upon themselves the duty in bringing peace in the Church.
This is the contribution of Constantine in the Council of Nicea to provide logistical support for the bishops. If we know our history we can easily debunk the allegations against the Church.
 John Schwarz, A Handbook Of The Christian Faith, p.153
 The Philocalian Calendar
 P. C Thomas, General Councils of the Church, Introduction