Many Christians cannot rightly divide the Word of God and so they are Double Minded in their Doctrine and Theology. As a result they are weak and ineffective.
In order to function properly as Christians we must know our function. Our function is revealed in the Gospel, the New Covenant.
Here is a list of the Bible Covenants:
1. Adamic Covenant. Found in Genesis 1:26-30 and Genesis 2:16-17 - this covenant is general in nature. It included the command not to eat from the tree of the knowledge of good and evil, pronounced a curse for sin, and spoke of a future provision for man's redemption (Genesis 3:15) .
2. Noahic Covenant. This general covenant was made between God and Noah following the departure of Noah, his family, and the animals from the ark. Found in Genesis 9:11 - "I establish my covenant with you, that never again shall all flesh be cut off by the waters of the flood, and never again shall there be a flood to destroy the earth." This covenant included a sign of God's faithfulness to keep it—the rainbow.
3. Abrahamic Covenant. This unconditional covenant - first made to Abraham in Genesis 12:1-3 - promised God's blessing upon Abraham, to make his name great and to make his progeny into a great nation. The covenant also promised blessing to those who blessed Abraham and cursing to those who cursed him. Further, God vowed to bless the entire world through Abraham's seed. Circumcision was the sign that Abraham believed the covenant (Romans 4:11). The fulfillment of this covenant is seen in the history of Abraham's descendants and in the creation of the nation of Israel. The worldwide blessing came through Jesus Christ, who was of Abraham's family line.
4. Palestinian Covenant. This unconditional covenant - found in Deut 30:1-10 - noted God's promise to scatter Israel if they disobeyed God, then to restore them at a later time to their land. This covenant has been fulfilled twice, with the Babylonian Captivity and subsequent rebuilding of Jerusalem under Cyrus the Great; and with the destruction of Jerusalem in A.D. 70, followed by the reinstatement of the nation of Israel in 1948.
5. Mosaic Covenant ( Old Covenant). This conditional covenant, found in Deut 11:1-32 and elsewhere, promised the Israelites a blessing for obedience and a curse for disobedience. Much of the Old Testament chronicles the fulfillment of this cycle of judgment for sin and later blessing when God's people repented and returned to God.
6. Davidic Covenant. This unconditional covenant - found in 2Sam 7:8-16 - promised to bless David's family line and assured an everlasting kingdom. Jesus is from the family line of David (Luke 1:32-33) and, as the Son of David (Mark 10:47,) is the fulfillment of this covenant.
7. New Covenant. This covenant - found in Jer 31:31-34 - promised that God would forgive sin and have a close, unbroken relationship with His people. The promise was first made to Israel and then extended to everyone who comes to Jesus Christ in faith (Matthew 26:28; Hebrews 9:15). -- Source: 
The Gospel is the Revelation of the New Covenant that Jeremiah foretold. It is the Power of God unto Salvation! Rom 1:16
It’s Much Better! by Barry Bennett
The book of Hebrews repeatedly uses the word “better” to describe the reality of our great salvation. Jesus is the guarantee of a better covenant:
By so much more Jesus has become a surety of a better covenant. (Heb 7:22)
This better covenant is established on better promises!
But now He has obtained a more excellent ministry, inasmuch as He is also Mediator of a better covenant, which was established on better promises. (Heb 8:6)
Jesus is the better sacrifice:
Therefore it was necessary that the copies of the things in the heavens should be purified with these, but the heavenly things themselves with better sacrifices than these. (Heb 9:23)
Our heavenly inheritance is better than anything we have on this earth:
Knowing that you have a better and an enduring possession for yourselves in heaven. (Heb 10:34)
Our covenant is sealed with Jesus’ perfect blood which is much better than the first human blood spilled in the earth, that of Abel.
To Jesus the Mediator of the new covenant, and to the blood of sprinkling that speaks better things than that of Abel. (Heb 12:24)
Let this better covenant do its work in you! All of God’s promises are “yes and amen.” Don’t stay on the fringes of your inheritance in Christ. Jump in and discover this better covenant!
Now may the God of peace who brought up our Lord Jesus from the dead, that great Shepherd of the sheep, through the blood of the everlasting covenant, make you complete in every good work to do His will, working in you what is well pleasing in His sight, through Jesus Christ, to whom be glory forever and ever. Amen. (Heb. 13:20-21)