“He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.” — John 3:18
If people hear about Jesus and reject Him, that's their business. If people have never heard about Jesus, telling them is our business.
People all over the world are dying completely unreached by Christians. As were we, they are condemned by their sin to eternal separation from God in the lake of fire. Here's the difference: Someone told us about Jesus, and we believed. No one has told them.
By His grace, God has made available, by His Word and through His Church, the message of His forgiveness through faith in Jesus Christ.
“…I am made all things to all men, that I might by all means save some.” — 1 Cor. 9:22b
Only this generation of Christians can share the Good News about Jesus Christ with this generation of people. Limited by time, we have an opportunity to invite people, as many as we will, to believe God.
“…the love of Christ constraineth us…” — 2 Corinthians 5:14a
We can do nothing about the people who have already passed into eternity. When we die, we will be unable to act in leading people to know God. While we live, we can intervene for some by sharing Christ.
“And that he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again.” — 2 Corinthians 5:15
We have the privilege and responsibility to act on behalf of others.
“Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ's stead, be ye reconciled to God.” — 2 Corinthians 5:20