The Bible says that salvation (or eternal life) is a FREE gift of God, and that anyone and everyone may receive this gift through obedience to the Gospel. But why should eternal life be free, when human beings in general will do almost anything to ensure that they are not killed, or die prematurely?
Ever since man was created, human beings have made all kinds of efforts to prolong life on earth, even looking for “the fountain of youth” or “the elixir of youth” or some such thing. Yet when the Gospel is preached, there is never a universal positive response to it. It is almost as though people think “This is too good to be true, so what’s the catch?”
Therefore unless people are shown from Scripture that the cost of our salvation was infinitely great, and the price which was paid could never be reckoned even in trillions of dollars, they will not undertstand why salvation is now offered by God freely through Christ.
While there are many Scriptures which explain what kind of price was paid, the best and most comprehensive passage is the 53rd chapter of Isaiah. It is not the prophet Isaiah who came up with this revelation, but it is God the Holy Spirit who gave those words to Isaiah.
ISAIAH ALREADY SAW THAT FEW WOULD BELIEVE HIS REPORT
1 Who hath believed our report? and to whom is the arm of the LORD revealed?
CHRIST WAS NOT IMMEDIATELY RECOGNIZED FOR WHO HE IS, THE SAVIOR OF THE WORLD
2 For he shall grow up before him as a tender plant, and as a root out of a dry ground: he hath no form nor comeliness; and when we shall see him, there is no beauty that we should desire him.
CHRIST WAS DESPISED AND REJECTED OF MEN, PARTICULARLY THE RELIGIOUS LEADERS
3 He is despised and rejected of men; a man of sorrows, and acquainted with grief: and we hid as it were our faces from him; he was despised, and we esteemed him not.
CHRIST WAS SMITTEN BY GOD THE FATHER AS NO MAN WAS EVER SMITTEN
4 Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted.
CHRIST TOOK ALL OUR SINS, INIQUITIES, AND GUILT UPON HIMSELF AND PAID THE FULLY PENALTY
5 But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed. 6 All we like sheep have gone astray; we have turned every one to his own way; and the LORD hath laid on him the iniquity of us all.
CHRIST -- THE LAMB OF GOD -- WAS LED AS AN UNPROTESTING LAMB TO THE SLAUGHTER
7 He was oppressed, and he was afflicted, yet he opened not his mouth: he is brought as a lamb to the slaughter, and as a sheep before her shearers is dumb, so he openeth not his mouth.
CHRIST WAS MADE SIN FOR US WHO KNEW NO SIN, THAT WE MIGHT BE MADE THE RIGHTEOUSNESS OF GOD IN HIM
8 He was taken from prison and from judgment: and who shall declare his generation? for he was cut off out of the land of the living: for the transgression of my people was he stricken.
CHRIST -- THE HOLY ONE OF GOD -- WAS CRUCIFIED BETWEEN CRIMINALS AS A CRIMINAL
9 And he made his grave with the wicked, and with the rich in his death; because he had done no violence, neither was any deceit in his mouth.
IT IS GOD THE FATHER -- NOT ANY MAN -- WHO MADE CHRIST AN OFFERING FOR SIN
10 Yet it pleased the LORD to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of the LORD shall prosper in his hand.
THE SUFFERIINGS OF CHRIST WOULD BE VINDICATED THROUGH THE OFFER OF SALVATION TO ALL
11 He shall see of the travail of his soul, and shall be satisfied: by his knowledge shall my righteous Servant justify many; for he shall bear their iniquities. [Note: "many" rather than "all" because all will not repent]
CHRIST MADE HIS BODY, SOUL, AND SPIRIT AN OFFERING FOR SIN
12 Therefore will I divide him a portion with the great, and he shall divide the spoil with the strong; because he hath poured out his soul unto death: and he was numbered with the transgressors; and he bare the sin of many, and made intercession for the transgressors.
Christ not only died for our sins, but He also rose again for our justification. Therefore sinners can be justified by grace through faith, and receive the gift of eternal life.
I rarely quote the KJV. That is not to say I never do, but my go-to is the Berean Study/Standard Bible 
