In the old testament, salvation was obtained by sacrifices.  Each year they would bring their sin offering (Exodus 29:14; Leviticus 4) to the priest and offer it for the atonement of their sins.  This offering would not allow their sins to be forgiven, but rather they would be covered for one year at which time they must bring another sin offering. 

In Leviticus 16:34 we find that the sin offering was for the "to make an atonement ..... for the children of the people."     What is this atonement? 

The word atonement comes from the Hebrew word "kaphar" [kaw-far’]  meaning "to cover, purge, make an atonement, make reconciliation, cover over with pitch;  to cover over, pacify, propitiate;  to cover over, atone for sin, make atonement for;  to cover over, atone for sin and persons by legal rites;  to be covered over;  to be covered." 

The atonement was not for the forgiveness of sin, but their guilt of the sin was covered over for one year (Exodus 30:10; Leviticus 16:34). 

The prophets down through the Old Testament have sought after and searched for the ultimate salvation which they had not yet found.  That salvation could not be had or understood until Jesus Christ had come to earth and lived among us.  Now, since his death and resurrection has come to pass, we can know, experience and understand of what salvation consists. 

The Holy Spirit had told the Prophets of the first coming of Christ, but they had no understanding and the salvation that He would provide by His existence here.  The did, however, know that Christ would be denied and abused (Isaiah 53:3-7 5).  They were given as much information as they needed but not informed with details, therefore, they didn't fully understand.  We today now have those details. 

The prophets foretold the New Covenant and the completeness of the blessings that comes with it.  Among them were the fullness of grace, anointing of the Holy Spirit, the fruits and gifts of the Holy Spirit and the ultimate redemptive process of which the law was a mere shadow.  These were all predicted in prophesy by the prophets of old. 

Having these things, we have something that even the angels are amazed with.  They have no concept of what redemption is all about.  They cannot be redeemed because they were originally created as the servants of God.  Those who have failed (devils) cannot be redeemed.  The angels "desire to look into" how we are so blessed that we have been given these wonderful gifts.