“In hope of eternal life, which God, that cannot lie, promised before the world began;”  
Titus 1:2

God promised eternal life before the world began, and every man has that light in himself:
“That was the true Light, which lighteth every man that cometh into the world.”  John 1:9
There is the expectation in every man for a better life; when all sin and suffering would cease, most assume it would have to happen after they leave this world, some presume it might be the life aliens leave in Mars, but God has already fulfilled his promise:
“But hath in due times manifested his word through preaching, which is committed unto me according to the commandment of God our Saviour;”  Titus 1:3
Eternal life is manifested through preaching, every time a Christian- the one whom God has committed the Gospel to- preaches to an unbeliever, he is making that promise available, he is giving the unbeliever the chance to have the longing of his heart met.
“And this is the record, that God hath given to us eternal life, and this life is in his Son.”  1 John 5:11
God has a testimony: the promise he made, he has fulfilled, eternal life is in his son! Once you receive Jesus into your heart, you’ve received his promise:
“He that hath the Son hath life; and he that hath not the Son of God hath not life.”  1 John 5:12
You have received a different kind of life and with that life comes the glorious commission to go and make that promise available to others! This is what they’ve been waiting for!!