"The essence of evangelism is not merely to talk about the cross but to proclaim the true doctrine of the cross. The purpose of the cross is not to arouse pity in us, neither is it merely some general display of the love of God. Not at all! It is finally understood only in terms of the law.
What was happening upon the cross was that our Lord and Saviour Jesus Christ, the Son of God, was enduring in His own holy body the penalty prescribed by the holy law of God for the sin of man. The law condemns sin, and the condemnation that it pronounces is death. "The wages of sin is death." The law pronounces that death must pass upon all who have sinned against God and broken His holy law. Christ says, "Think not that I am come to destroy the law, or the prophets; I am not come to destroy, but to fulfil." One of the ways in which the law has to be fulfilled is that its punishment of sin must be carried out. This punishment is death, and that was why He died. The law must be fulfilled."
Actually, if you read this carefully, Martyn Lloyd-Jones was explaining why Jesus must die and I fully agree with his explanation. However, he was not explaining why Jesus must die on the cross, and not by any other way eg. by stoning which is the punishment for blasphemy, which Jesus was accused of (Matt 26:65), under the Law (Lev 24:16, John 10:33).
Some people have said that Jesus died on the cross because that was how the Romans executed criminals during that time but that does not explain the spiritual significance of the cross. Considering the kind of extreme whipping that Jesus received from the Roman soldiers, Jesus could very well have died from the whipping and still fulfilled His task of paying the wages of sin of the world. So, why must Jesus die on the cross?
Gal 3:21 says "Christ redeemed us from the curse of the law by becoming a curse for us, for it is written: "Cursed is everyone who is hung on a tree."" This verse is very clear - Jesus must die on the cross to redeem us from the curse of the law. Yes, the law is holy and the commandments holy, righteous and good (Rom 7:12), and the law is not based on faith; on the contrary, "The man who does these things will live by them." (Gal 3:12) Hence, those under the law were perpetually cursed because it was impossible for them to keep the law since whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it (James 2:10).
Do you know how many curses there are under the law? Read on:
15 “But it shall come to pass, if you do not obey the voice of the LORD your God, to observe carefully all His commandments and His statutes which I command you today, that all these curses will come upon you and overtake you:
16 “Cursed shall you be in the city, and cursed shall you be in the country.
17 “Cursed shall be your basket and your kneading bowl.
18 “Cursed shall be the fruit of your body and the produce of your land, the increase of your cattle and the offspring of your flocks.
19 “Cursed shall you be when you come in, and cursed shall you be when you go out.
20 “The LORD will send on you cursing, confusion, and rebuke in all that you set your hand to do, until you are destroyed and until you perish quickly, because of the wickedness of your doings in which you have forsaken Me. 21 The LORD will make the plague cling to you until He has consumed you from the land which you are going to possess. 22 The LORD will strike you with consumption, with fever, with inflammation, with severe burning fever, with the sword, with scorching, and with mildew; they shall pursue you until you perish. 23 And your heavens which are over your head shall be bronze, and the earth which is under you shall be iron. 24 The LORD will change the rain of your land to powder and dust; from the heaven it shall come down on you until you are destroyed.
25 “The LORD will cause you to be defeated before your enemies; you shall go out one way against them and flee seven ways before them; and you shall become troublesome to all the kingdoms of the earth. 26 Your carcasses shall be food for all the birds of the air and the beasts of the earth, and no one shall frighten them away. 27 The LORD will strike you with the boils of Egypt, with tumors, with the scab, and with the itch, from which you cannot be healed. 28 The LORD will strike you with madness and blindness and confusion of heart. 29 And you shall grope at noonday, as a blind man gropes in darkness; you shall not prosper in your ways; you shall be only oppressed and plundered continually, and no one shall save you.
30 “You shall betroth a wife, but another man shall lie with her; you shall build a house, but you shall not dwell in it; you shall plant a vineyard, but shall not gather its grapes. 31 Your ox shall be slaughtered before your eyes, but you shall not eat of it; your donkey shall be violently taken away from before you, and shall not be restored to you; your sheep shall be given to your enemies, and you shall have no one to rescue them. 32 Your sons and your daughters shall be given to another people, and your eyes shall look and fail with longing for them all day long; and there shall be no strength in your hand. 33 A nation whom you have not known shall eat the fruit of your land and the produce of your labor, and you shall be only oppressed and crushed continually. 34 So you shall be driven mad because of the sight which your eyes see. 35 The LORD will strike you in the knees and on the legs with severe boils which cannot be healed, and from the sole of your foot to the top of your head.
36 “The LORD will bring you and the king whom you set over you to a nation which neither you nor your fathers have known, and there you shall serve other gods—wood and stone. 37 And you shall become an astonishment, a proverb, and a byword among all nations where the LORD will drive you.
38 “You shall carry much seed out to the field but gather little in, for the locust shall consume it. 39 You shall plant vineyards and tend them, but you shall neither drink of the wine nor gather the grapes; for the worms shall eat them. 40 You shall have olive trees throughout all your territory, but you shall not anoint yourself with the oil; for your olives shall drop off. 41 You shall beget sons and daughters, but they shall not be yours; for they shall go into captivity. 42 Locusts shall consume all your trees and the produce of your land.
43 “The alien who is among you shall rise higher and higher above you, and you shall come down lower and lower. 44 He shall lend to you, but you shall not lend to him; he shall be the head, and you shall be the tail.
45 “Moreover all these curses shall come upon you and pursue and overtake you, until you are destroyed, because you did not obey the voice of the LORD your God, to keep His commandments and His statutes which He commanded you. 46 And they shall be upon you for a sign and a wonder, and on your descendants forever.
47 “Because you did not serve the LORD your God with joy and gladness of heart, for the abundance of everything, 48 therefore you shall serve your enemies, whom the LORD will send against you, in hunger, in thirst, in nakedness, and in need of everything; and He will put a yoke of iron on your neck until He has destroyed you. 49 The LORD will bring a nation against you from afar, from the end of the earth, as swift as the eagle flies, a nation whose language you will not understand, 50 a nation of fierce countenance, which does not respect the elderly nor show favor to the young. 51 And they shall eat the increase of your livestock and the produce of your land, until you are destroyed; they shall not leave you grain or new wine or oil, or the increase of your cattle or the offspring of your flocks, until they have destroyed you.
52 “They shall besiege you at all your gates until your high and fortified walls, in which you trust, come down throughout all your land; and they shall besiege you at all your gates throughout all your land which the LORD your God has given you. 53 You shall eat the fruit of your own body, the flesh of your sons and your daughters whom the LORD your God has given you, in the siege and desperate straits in which your enemy shall distress you. 54 The sensitive and very refined man among you will be hostile toward his brother, toward the wife of his bosom, and toward the rest of his children whom he leaves behind, 55 so that he will not give any of them the flesh of his children whom he will eat, because he has nothing left in the siege and desperate straits in which your enemy shall distress you at all your gates. 56 The tender and delicate woman among you, who would not venture to set the sole of her foot on the ground because of her delicateness and sensitivity, will refuse to the husband of her bosom, and to her son and her daughter, 57 her placenta which comes out from between her feet and her children whom she bears; for she will eat them secretly for lack of everything in the siege and desperate straits in which your enemy shall distress you at all your gates.
58 “If you do not carefully observe all the words of this law that are written in this book, that you may fear this glorious and awesome name, THE LORD YOUR GOD, 59 then the LORD will bring upon you and your descendants extraordinary plagues—great and prolonged plagues—and serious and prolonged sicknesses. 60 Moreover He will bring back on you all the diseases of Egypt, of which you were afraid, and they shall cling to you. 61 Also every sickness and every plague, which is not written in this Book of the Law, will the LORD bring upon you until you are destroyed. 62 You shall be left few in number, whereas you were as the stars of heaven in multitude, because you would not obey the voice of the LORD your God. 63 And it shall be, that just as the LORD rejoiced over you to do you good and multiply you, so the LORD will rejoice over you to destroy you and bring you to nothing; and you shall be plucked from off the land which you go to possess.
64 “Then the LORD will scatter you among all peoples, from one end of the earth to the other, and there you shall serve other gods, which neither you nor your fathers have known—wood and stone. 65 And among those nations you shall find no rest, nor shall the sole of your foot have a resting place; but there the LORD will give you a trembling heart, failing eyes, and anguish of soul. 66 Your life shall hang in doubt before you; you shall fear day and night, and have no assurance of life. 67 In the morning you shall say, ‘Oh, that it were evening!’ And at evening you shall say, ‘Oh, that it were morning!’ because of the fear which terrifies your heart, and because of the sight which your eyes see.
68 “And the LORD will take you back to Egypt in ships, by the way of which I said to you, ‘You shall never see it again.’ And there you shall be offered for sale to your enemies as male and female slaves, but no one will buy you.”
Quite a long list, isn't it? Do we need to be concerned about all these curses? No, because Christ has redeemed us from the curse of the law. I recommend that you listen to Pastor Joseph Prince's sermon "The Significance of the Cross" (which is my favourite sermon, by the way) for a detailed explanation of why Jesus must die on the cross.
One final question: Why did Jesus redeem us from the curse of the law?
He redeemed us in order that the blessing given to Abraham might come to the Gentiles through Christ Jesus, so that by faith we might receive the promise of the Spirit.
Gal 3:14 (NIV)