"If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed:" (2 John 10)
This verse may sound harsh, but there can be no compromise about the Gospel of grace (Galatians 1:6)
"3But neither Titus, who was with me, being a Greek, was compelled to be circumcised: 4And that because of false brethren unawares brought in, who came in privily to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage: 5To whom we gave place by subjection, no, not for an hour; that the truth of the gospel might continue with you." (Galatians 2: 3-5)
There is no compromise when we accept that we are saved by all that Jesus did, and not by one thing that we can do:
"4But God, who is rich in mercy, for his great love wherewith he loved us, 5Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) 6And hath raised us up together, and made us sit together in heavenly places in Christ Jesus: 7That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus. 8For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:" (Ephesians 2: 4-8)
We are saved by grace, through faith, and not by any works of our own.
We cannot save ourselves. We were born dead in trespasses, and the life that we need, must come from outside of us:
"But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us. 9Much more then, being now justified by his blood, we shall be saved from wrath through him." (Romans 5: 8-9)
We were still sinners, we were not paying attention, we did not care one bit about God, and Paul even writes that we were alienated against God in our minds (Ephesians 2: 1)
Because this verse ties in with the prior verse, which speaks of abiding in the Doctrine of Christ, we must not permit anyone to dilute the fresh understanding of God's grace in our lives.
There is no room for mixture, and we should not mix with people who insist on doing the same:
"Woe to them! They have taken the way of Cain; they have rushed for profit into Balaam's error; they have been destroyed in Korah's rebellion." (Jude 11)
The way of Cain, by the way, is the path of self-righteousness, trying to earn God's approval through our actions rather than trusting in the perfect sacrificial lamb, which Abel demonstrated as a type:
"12Not as Cain, who was of that wicked one, and slew his brother. And wherefore slew he him? Because his own works were evil, and his brother's righteous." (1 John 3: 12)
And why were Cain's works evil? Presenting your own efforts as righteousness is the height of arrogant pride. Period.
Do not associate with anyone who seeks to bring you into condemnation, who insists on bringing back the law, the bondage of the Ten Commandments, whose time had come, but has now been replaced by Christ and Him Crucified.