The Bible clearly tells us to spread the Gospel. Matthew 28:19 says Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Many of of know that verse and it comes to mind as soon as we think of missions. I've been in churches that have a sign over the main door stating "You are now entering into the mission field" as you leave. But, do you really know the consequences of NOT telling others?
Ezekiel 3:18 -19 When I say unto the wicked, Thou shalt surely die; and thou givest him not warning, nor speakest to warn the wicked from his wicked way, to save his life; the same wicked man shall die in his iniquity; but his blood will I require at thine hand. Yet if thou warn the wicked, and he turn not from his wickedness, nor from his wicked way, he shall die in his iniquity; but thou hast delivered thy soul.
God is talking to Ezekiel about the children of Israel. HE knows they are stubborn and hard headed and hard hearted, but He tells Ezekiel to witness to them anyway. (Does that sound familiar?) This passage tells us that if we do not tell others the truth that we have, and that person dies and goes to hell, their blood is on our hands. What a heavy burden! We are commanded to tell others, and this is the punishment of not being obedient.