And what will be the judgment of God outside the Church of Christ? Christ said that the branch that will be cast out will be thrown into the fire.

6 If anyone does not abide in Me, he is cast out as a branch and is withered; and they gather them and throw them into the fire, and they are burned. (John 15:6, ibid)

The branches referred to by Christ are the members of His Body the Church. As these branches will be cast out, they will be thrown into the fire.

If Christ will save His Church alone, is there any invitation of Christ to men for them to be saved on the day of judgment? Yes. Christ invited men to enter by Him.

9 I am the door. If anyone enters by Me, he will be saved, and will go in and out and find pasture. (John 10:9, ibid)

Those who enter Christ became parts of Christ's body.

27 Now you are the body of Christ, and members individually. (I Corinthians 12:27, ibid)

The body of Christ is His own Church (Colossians 1:18, Romans 16:16).

Therefore: The main purpose why Christ founded His Church, is to save those who are inside His Church from the wrath of God on Judgment Day.

So, if you want to be saved on the day of Judgment, you must enter Christ, by becoming members of the true Church of Christ.