The new covenant is an agreement that God has made with man, "signed with Jesus' blood" ( Heb.13:20 - Living). Now we have to put our signature on it with the blood of our Self-life. There is no other way to enter into that agreement with God. It is because many do not sign on the dotted line with the blood of their Self-life that they never enter into a satisfying Christian life.
Jesus' covenant with His Father throughout His life was that He would never once use His body to do His own will (Heb.10:5ff). He would put his own will to death and thus He signed that covenant with the "blood" (crucifixion) of His own will. We are now called to fellowship with Him in the same way. This way is not a strain to walk in at all. On the contrary it will lead you to the happiest life (free from strain) that you can ever live. It is to this covenant that we testify when we get baptized and also when we break bread together.
The new wine that Jesus spoke of inLuke 5:38, refers to the life of God that we can partake of under the new covenant. The old wine refers to the life under the Law - a life of rules and regulations. The two trees in the Garden of Eden also symbolize life under these two covenants. A life held back from sin (and looking apparently upright) by many rules and regulations (as found in cult-groups) leads to death, as God warned Adam about the tree of knowledge of good and evil. True Christianity is a life that springs from partaking of the life of Jesus within, that warns us that certain things are dirty and certain other things are clean. We have freedom of choice, but we don't avoid things because we are bound by any rules ("Touch not, taste not" - Col.2:21 ), or to impress other people.
The new wineskin speaks of the Body of Christ, which is built, when we present our body to Him as a living sacrifice every day, and ask Him to fill us with the Holy Spirit, so that the same work that the Spirit did in Jesus' body in His earthly days can be done in us too. This makes us one with others who are walking the same way. Thus we are made into one body in Christ, the church, in which He equips us with gifts necessary to build one another up.
Thus Satan is crushed under our feet (Rom.16:20). When we give room to Satan to accuse us or to make us feel guilty, then he sits on our head. But his place is under our feet.
Sin is defined (in Rom.3:23 ) as coming short of God's glory - and God's glory was seen in the life of Jesus. So remember that
"Anything that we cannot do in fellowship with Jesus is sin.
Under the old covenant, sin could only be covered (by the blood of bulls and goats), and not removed (Psa.32:1,2). It could not be cleansed or blotted out. There was a constant remembrance of it year after year (Heb.10:3,4). Under the new covenant however all our sin is not only cleansed by Jesus' blood, but God promises that He will never remember them any more (Heb.8:12). You must understand this difference between the two covenants clearly.