Galatians 1:9

I repeat what I have already said: If any person preaches to you a "gospel" other than what you have already received [from us apostles], he should be cut off from God's [salvation].

Romans 16:17

Now I urge you, brothers, watch out for those who are causing divisions and occasions for falling [away from God over matters] contrary to the teaching you have learned, and withdraw from them [i.e., stop listening to their false teaching].

2 Corinthians 1:17

So, when I made this decision, was I just vacillating [in uncertainty]? Or, do I make plans in a worldly way [i.e., just to suit my own fancy], so that my "yes" and "no" [do not really mean anything]?

2 Corinthians 13:1-2

This will be my third visit to you. [Deut. 19:15 says], "Every matter should be settled by the testimony of two or three witnesses."

Philippians 3:1

Finally, my brothers, rejoice in [your relationship to] the Lord. It does not trouble me to write the same things to you again, because you will be safer if I do. [Note: These "same things" may refer to warnings against false teachers which Paul had either spoken to them or written about previously].

Philippians 4:4

Rejoice in [fellowship with] the Lord all the time. I will say it again: Rejoice!

Revelation 22:18-19

I testify to every person who hears the words of the prophecy of this book [Note: This is probably Jesus speaking, but could possibly be John]. If anyone adds to these words, God will add to him the calamities described in this book.

Treasury of Scripture Knowledge

Summary

As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed.

General references

Bible References

So

2 Corinthians 1:17
So, when I made this decision, was I just vacillating [in uncertainty]? Or, do I make plans in a worldly way [i.e., just to suit my own fancy], so that my "yes" and "no" [do not really mean anything]?
2 Corinthians 13:1
This will be my third visit to you. [Deut. 19:15 says], "Every matter should be settled by the testimony of two or three witnesses."
Philippians 3:1
Finally, my brothers, rejoice in [your relationship to] the Lord. It does not trouble me to write the same things to you again, because you will be safer if I do. [Note: These "same things" may refer to warnings against false teachers which Paul had either spoken to them or written about previously].
Philippians 4:4
Rejoice in [fellowship with] the Lord all the time. I will say it again: Rejoice!

Than

Revelation 22:18
I testify to every person who hears the words of the prophecy of this book [Note: This is probably Jesus speaking, but could possibly be John]. If anyone adds to these words, God will add to him the calamities described in this book.

General references

1 Corinthians 3:11
For no one can lay [any] other foundation than the one which [God] has [already] laid, which is Jesus Christ.