Mark 16:15 tells us to “Go into all the world and preach the gospel…”.
In John 14:15, Jesus told his disciples, “If you love Me, you will keep My commandments”.
God is holy and righteous and hates sin. Still, God loves the people that he created. He’s made salvation available through Jesus Christ. Unless people hear and believe the gospel, they will receive the judgement of God. Because He is a holy God, He cannot receive sinners until they’re redeemed.
Christ didn’t command all people to be missionaries, but He DID instruct all believers to be faithfully involved in discipling all nations. Lost souls will face the final judgement of God for their sins – eternal separation from God. Without missions, those who sit in darkness have no opportunity to see the light. They have no alternative.
As we desire to demonstrate our love (John 14:15) and our obedience (Mark 16:15) to the Lord, it’s our responsibility to “reach out” to those in darkness. If not in person, our responsibility is financial support, prayer and encouragement to those who are called to the field.