The Gospel is that work that Jesus did in our name and on our behalf that justifies the ungodly, Romans 4:5 and reconciles us and the world unto God, 2 Corinthians 5:18, 19.
Paul said that the Gospel... "Is the power of God unto salvation to every one that believes" Romans 1:16.
The Gospel of Jesus Christ is all that one needs to be saved. Faith in Christ and his Gospel is the entrance into eternal life. Religion, whether it be the Calvinist religion or the Catholic religion or whatever religion is not the way. Religion is the broadway that leads to destruction and "Many there be that go that way" Matthew 7:13.
There was no religion in the early church. What there was, was people that wanted to live according to rules and laws. Paul was continually preaching against living this way. Paul taught that "The Just Shall Live By Faith" Romans 1:17. and not by rules and laws. To live by faith is to live by faith in Christ and his Gospel.
It is not the Gospel plus Calvinism or The Gospel plus Catholicism. It is the Gospel plus nothing. Jesus saves and he saves to the uttermost, "Wherefore he is able also to save them to the uttermost, that come unto God by Jesus Christ" Hebrews 7:25.
Is your religion able to save you to the uttermost? Religion is a diversion away from Christ and his Gospel. There is no Spirit in religion. Religion is anti-Christ and anti-Gospel. The Holy Spirit is only given to those who are trusting in Christ and his Gospel for their salvation. "This only would I learn of you, did you receive the Spirit by the works of the law (Religion) or by the hearing of faith" Galatians 3:2. Which is the Gospel.