Here is a succinct quote from John Calvin about what he believed we should tell people about the Gospel.

That man was alienated from God by sin, an heir of wrath, liable to the punishment of eternal death, excluded from all hope of salvation, a total stranger to the blessing of God, a slave to Satan, a captive under the yoke of sin, and, in a word, condemned to and already involved in, a horrible destruction; that, in this situation, Christ interposed as an intercessor; that He has taken upon Himself and suffered the punishment which by the righteous judgment of God impended over all sinners; that by His blood He has expiated those crimes which make them odious to God; that by this expiation God the Father has been duly satisfied and atoned; that by this intercessor His wrath has been appeased; that this is the foundation of peace between God and men; and that this is the bone of His benevolence towards them.

Source: Portrait of Calvin by T.H.L. Parker