The finality of the Cross is a serious matter.
Either we believe it, or we do not believe it.
The one work which Jesus preached to the Jews of His earthly ministry, and to all of us today, is "believe":
"Then said they unto him, What shall we do, that we might work the works of God? 29Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent." (John 6: 28-29)
Jesus did not come to bring us rules, but to establish the New Covenant:
"And it shall be for a sign and for a witness unto the LORD of hosts in the land of Egypt: for they shall cry unto the LORD because of the oppressors, and he shall send them a saviour, and a great one, and he shall deliver them." (Isaiah 19: 20)
"33But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people. 34And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD: for I will forgive their iniquity, and I will remember their sin no more." (Jeremiah 31: 33-34)
"Rejoice greatly, O daughter of Zion; shout, O daughter of Jerusalem: behold, thy King cometh unto thee: he is just, and having salvation; lowly, and riding upon an ass, and upon a colt the foal of an ass." (Zechariah 9: 9)
What did this Savior do for us? He came to save us from sin and bring us into reconciliation with our Father:
"4Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted.
"5But 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." (Isaiah 54: 4-5)
Now, this spirit of grace is essential for us, because we are dead, in need of life, which we can only receive from Him who has been from the beginning (1 John 2:12-14).
For this reason, Jesus rebuked the Pharisees:
"But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation:" (Mark 3: 29)
Man is condemned already because of Adam's sin (John 3: 18), and that is not God's fault, for God has given us His son that we may reign in life through Him (Romans 5: 17).
If we reject His perfect sacrifice, if we do not receive Jesus' life, then we are dead forever, and there is no way out.
Do not reject the Spirit of Grace. Do not treat the blood of Jesus like a common thing, and rest in the truth that He did a perfect job of cleansing away your sins, and that His blood continues to do so (1 John 1: 7).