Taken in context, the Apostle Paul used it thusly: "Being justified freely by His grace through the redemption that is in Christ Jesus, 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; to declare, [I say], at this time His righteousness: that He might be just, and the justifier of Him which believeth in Jesus" (Rom. 3:24-26).
Here is how the Apostle John used it. "My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: and He is the propitiation for our sins: and not for ours only, but also for [the sins of] the whole world" (1 Jn. 2:1-2). Again, in 1 John 4:9-10, he wrote, "In this was manifested the love of God toward us, because that God sent His only begotten Son into the world, that we might live through Him. Herein is love, not that we loved God, but that He loved us, and sent His Son [to be] the propitiation for our sins."
The writer of Hebrews wrote, "Which had the golden censer, and the ark of the covenant overlaid round about with gold, wherein [was] the golden pot that had manna, and Aaron's rod that budded, and the tables of the covenant; and over it the cherubims of glory shadowing the mercy seat; of which we cannot now speak particularly (9:4-5).
Paul compared the scope of the consequences of Adam's sin, to the scope of the payment for sin by Jesus in Romans 5:19: "For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous." Some have said that the word "many" does not encompass all, but if Adam's sin brought about death to all, then Jesus' death made righteousness available to all.
I see it as being like a man walking into a bank and paying off all the loans of every customer. All the customers are declared debt free. However, there are many who believe that no one gets anything for nothing. They see the payment of their debt as being too good to be true, so they continue to make payments, even though the bank repeatedly tells them it is no longer necessary. Sad, isn't it.
Religious works are man's effort to pay a non-existing debt.