Saint Irenaeus of Lyons
During the second century, the Catholic Church continued in its battle against the Gnostic sects. The Gnostics believed that human salvation was accomplished through secret knowledge. They gained their name from Greek word "gnosis" meaning "knowledge."
Saint Irenaeus was a Greek and bishop of Lyons. He was reputed to be a disciple of Saint Polycarp.
The battleground text between the Catholics and the Gnostics was Saint Paul's 1 Corinthians. This is the most often quoted epistle in debates with the Gnostics. 1 Corinthians 15:50 is the most controversial verse, as it reads:
“Now this I say, brethren, that flesh and blood cannot possess the kingdom of God: neither shall corruption possess incorruption.” (1 Corinthians 15:50, D-R)
The Gnostics claimed that this verse "proved" that Christ did not have a true physical body, that the Eucharist could not then be His true body, and that there would be no final resurrection at the end of the world.
Notice that heretics often appeal to Sacred Scripture, and especially to Saint Paul.
The Gnostics believed that "Christ" and the historical Jesus were two separate realities that united at Christ's baptism. The "Christ," they said, became united to the historical man Jesus. For them, the the spiritual Christ, not the man, is the focus of Saint Paul's theology.
The reply of Saint Irenaeus (and the Catholic Church throughout time) is to always study Scripture in context. Heretics always lift singular verses from context and argue from them. This is not the Catholic way. Catholic theologians read Scripture in the context of Scripture and in the context of Tradition. It's a much broader approach to theology.
The answer to the Gnostics, then, is to look at 1 Cor 15 with a wider lens. In the same chapter, we find:
“And if Christ be not risen again, then is our preaching vain: and your faith is also vain.” (1 Corinthians 15:14, D-R)
And if the Gnostic should claim that Paul is only referring to the "spiritual Christ," one need only to refer to Romans:
“Who was predestinated the Son of God in power, according to the spirit of sanctification, by the resurrection of our Lord Jesus Christ from the dead:” (Romans 1:4, D-R)
The Catholic Church is catholic both because she is universal, but also because she holds to the Faith wholly and entirely - kata holos.