"If you belonged to the world, it would love you as its own. As it is, you do not belong to the world, but I have chosen you out of the world. That is why the world hates you."
Jesus has not made it a secret what we must do but has revealed everything necessary and sufficient for our salvation. Actually, it isn't a question of "What must we do?" but rather "Who must we know?". But who can know the Father except those to whom the Father has revealed himself? Those who do not belong to him do not see him, but his sheep recognize his voice.
Not everyone will be saved on that great and terrible day and we have no time to waste. Jesus had three years to complete his mission and never once is he seen begging and pleading with people to believe. They either did or they did not believe. He didn't have time to waste when there were others who were willing to listen who have not heard. It's a hard reality, but unless we can accept that some will perish, we will never get around to reaching everyone else.
The ship is sinking and this world is passing away. God has given us lifeboats, but if no one believes our message that the ship is sinking but there's a way out, how can they be saved? So we press on to find those who will believe our message and pray those who do not believe come to their senses before it's too late.