God declared a covenant between Himself and Abraham and with the seed of his son with Sarah, Isaac as explored in "The Old Covenant" video:
http://islamchristianforum.com/index.php?topic=519.0Gen 17:19
And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, [and] with his seed after him. Later on, during that Old Covenant, God had Jeremiah prophesy of a new covenant many hundreds of years before Jesus fulfilled the old covenant:
OT
Jeremiah 31:31
Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah: 32 Not according to the covenant that I made with their fathers in the day [that] I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the LORD: {although...: or, should I have continued an husband unto them?} 33 But 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. This new covenant was fulfilled through Jesus Christ through whom God manifest, or revealed, Himself to mankind to show us the WAY to come to Him. The law is IN our inward parts:
NT
1Cr 3:16
Know ye not that ye are the temple of God, and [that] the Spirit of God dwelleth in you? 1Cr 6:19
What? know ye not that your body is the temple of the Holy Ghost [which is] in you, which ye have of God, and ye are not your own? That is how Jesus fulfilled the law.
Hbr 12:24
And to Jesus the mediator of the new covenant, and to the blood of sprinkling, that speaketh better things than [that of] Abel. The
one perfect sacrifice of the only sinless person in world history.
John 1:29
The next day John seeth Jesus coming unto him, and saith, Behold the Lamb of God, which taketh away the sin of the world.Mat 26:28
For this is my blood of the new testament, which is shed for many for the remission of sins.John 3:16
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. The fulfillment in God's people:
Gal 5:14
For all the law is fulfilled in one word, [even] in this; Thou shalt love thy neighbour as thyself. Hbr 8:13
In that he saith, A new [covenant], he hath made the first old. Now that which decayeth and waxeth old [is] ready to vanish away. Jesus is the mediator of that new covenant:
1Ti 2:5
For [there is] one God, and one mediator between God and men, the man Christ Jesus; Indeed Jesus has been the mediator between God and mankind from our beginning. The way God chose to reveal Himself to us in a way that our limited human understanding could comprehend.
Hbr 9:26
For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself. After Jesus was resurrected He declared:
Mat 28:18
And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth. 19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: OT
Back to Jeremiah's prophecy in 31:34
And 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.NT
Rom 3:25
Whom God hath set forth [to be] a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; All who believe in Jesus shed blood are saved from sin.
Mat 26:28
For this is my blood of the new testament, which is shed for many for the remission of sins.Hbr 9:22
And almost all things are by the law purged with blood; and without shedding of blood is no remission. No man took Jesus life:
John 10:17
Therefore doth my Father love me, because I lay down my life, that I might take it again. 18 No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father. In the Old Testament book of Psalms we find Jesus' crucifixion prophesied:
OT
Psalms 22:16
For dogs have compassed me: the assembly of the wicked have inclosed me: they pierced my hands and my feet. 17 I may tell all my bones: they look [and] stare upon me. 18 They part my garments among them, and cast lots upon my vesture. Fulfilled:
NT
Matthew 27:35
And they crucified him, and parted his garments, casting lots: that it might be fulfilled which was spoken by the prophet, They parted my garments among them, and upon my vesture did they cast lots. We find another reference in Old Testament prophecy of the end:
OT
Zechariah 12:8
In that day shall the LORD defend the inhabitants of Jerusalem; and he that is feeble among them at that day shall be as David; and the house of David [shall be] as God, as the angel of the LORD before them. 9 And it shall come to pass in that day, [that] I will seek to destroy all the nations that come against Jerusalem. 10 And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for [his] only [son], and shall be in bitterness for him, as one that is in bitterness for [his] firstborn.John 19:37
And again another scripture saith, They shall look on him whom they pierced. The same Koine Greek word diatheke is translated as "testament" 13 times and "covenant" 20 times.
testament
New Testament Greek Definition:
1242
diatheke {dee-ath-ay'-kay}
from 1303; TDNT - 2:106,157; n f
AV -
covenant 20,
testament 13; 33
1) a disposition, arrangement, of any sort, which one wishes to
be valid, the last disposition which one makes of his earthly
possessions after his death, a testament or will
2) a compact, a covenant, a testament
2a) God's covenant with Noah, etc.