The apostle Paul crystallizes the whole concept of the gospel in 2 Cor 5:19 which says, “God was in Christ, reconciling the world unto himself.” In that text we see that God is the one that is taking responsibility. But how?
Well of course we understand He sent His Son, the second person of the Trinity. The Lord Jesus Christ came as God the Son into the world, and He took flesh, and as Gal 4:4 puts it, “He was made of a woman, made under the law” i.e. He was made subject to the conditions that man is under. And He took the responsibility as our substitute to live for us, to die for us, and then validated His work by His resurrection.
And that essentially is the gospel, and the way we receive what God has done is by believing. This is the work of God, that ye believe on Him whom He hath sent.