The book of Hebrews is rich with explanations. Why did Jesus have to die to save us? Or, maybe you’ve never thought about why the Bible is divided into The Old Testament and the New Testament. There may be other people that are able to cover this more thoroughly than I can, but this makes perfect sense to me. More often than not, rich people and some who are poor that have something valuable to leave, prepare a last will and testament to help procure the distribution of their valuables upon their death. As long as they are alive, their will can be changed, revoked or altered. If a receiver of the valuables makes an enemy of the one making the will, they could lose their inheritance. The will is not set in stone until the one who made the testament is dead. So, the New Testament is the last will and testament of our Savior Jesus Christ! In order for it to go into effect, He had to die. I would go on to say that those who die without accepting their portion of their inheritance, which is eternal life, lose - big time!
For where a will is involved, the death of the one who made it must be established. For a will takes effect only at death, since it is not in force as long as the one who made it is alive. Hebrews 9:16-17