Heidelberg Catechism · 1563

Q30. Do those believe in the only Saviour Jesus who seek their salvation and well-being from saints, in themselves, or anywhere else?

No. Though they boast of Him in words, they in fact deny the only Saviour Jesus. For one of two things must be true: either Jesus is not a complete Saviour, or those who by true faith accept this Saviour must find in Him all that is necessary for their salvation.
Answer · Heidelberg Catechism

Scripture proofs

  1. [1]
    1 Corinthians 1:12-13

    Now this I say, that every one of you saith, I am of Paul; and I of Apollos; and I of Cephas; and I of Christ. Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul?

    Galatians 5:4

    Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.

  2. [2]
    Colossians 1:19-20

    For it pleased the Father that in him should all fulness dwell; And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven.

    Colossians 2:10

    And ye are complete in him, which is the head of all principality and power:

    1 John 1:7

    But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.

Proof texts as given in the original; verse text from the King James Version.