Many people who argue universalism like to present the vague idea of “God” as being the Father, and try to teach that, despite not believing in Jesus or the Holy Spirit, a person is still saved for their faith in the Father. This is especially true among “hopeful universalists” who try to argue that Jews and Muslims will still go to heaven because of their belief in “God,” despite their denial of the divinity and individual Personhood of the Son and Holy Spirit.
My usual argument against this boils down to a metaphor: the Trinity is not a buffet. That is, a person cannot decide that they want the Father – but not the Son and Holy Spirit. The individual Persons represent the fullness of the deity, and to deny one is to deny them all. This is both theologically, confessionally, and – most importantly – scripturally sound. In this regard, I went and dug up this quote by late fourth century Church Father Basil the Great, taken from his work On the Holy Spirit.
Who has woe? Who are afflicted? Who are headed for agony, darkness, eternal damnation? The transgressors; those who deny the faith. What is the proof of their denial? They have abandoned what they professed when they entered God’s household. What did they profess? Faith in the Father, the Son, and the Holy Spirit. They uttered these saving words when they renounced the devil and his angels. How can the children of light describe such men? They are transgressors, since they have broken the saving covenant. What else can denying God, denying Christ, be called, but transgressing? How do you wish me to label those who deny the Spirit? They must be described in the same way, for they have broken their covenant with God. Professing faith in Him wins the blessings of true religion, but damnation will be the wages of the godless who have denied Him. To forsake the profession of faith is a fearful thing, and they have abandoned it not through fear of fire, or sword, or cross, or flogging, or the wheel, or the rack, but only because they have been led astray by the deceitful sophistries of the Spirit-deniers. I swear to every man who confesses Christ but denies the Father: Christ will profit him nothing. If a man calls upon God, but rejects the Son, his faith is empty. If someone rejects the Spirit, his faith in the Father and the Son is made useless; it is impossible to believe in the Father and the Son without the presence of the Spirit. He who rejects the Spirit rejects the Son, and he who rejects the Son rejects the Father. “No one can say ‘Jesus is Lord’ except in the Holy Spirit” [1 Cor 2:3], and “no one has ever seen God; the only-begotten God, who is in the bosom of the Father, He has make Him known” [John 1:18]. Such a person has no part in true worship. It is impossible to worship the Son except in the Holy Spirit; it is impossible to call upon the Father except in the Spirit of adoption.