My little children, I am writing these things to you so that you may not sin. But if anyone does sin, we have an advocate with the Father, Jesus Christ the righteous. He is the propitiation for our sins, and not for ours only but also for the sins of the whole world. (1 John 2:1-2)
Two things jump out here and they are two very important doctrines that are kind of glossed over: The idea of Christ as advocate and the idea of Christ as propitiation.
Christ as Advocate
Men naturally like the idea of human intermediaries. Praying in the name of Christ seems OK, but it just seems more real to us if we have someone else we can see and touch. But when man sins, as man will, there is only one person we can turn to, only one we can trust and only one who is able to act as advocate and intermediary for us: Jesus Christ. There is no longer a Levitical priesthood needed or desired to acts as priests for us. We have a High Priest and His name is Jesus Christ and we need and desire no other. Every Christian has this same advocate in Christ, so we do not have to go to a pastor or confess to a priest or pray to a dead "saint" or light candles or any other of the myriad of religious rituals we have created to try to gain favor with God. All the favor and righteousness we will ever need has been bought with a price by Christ at the cross and He stands at the right hand of the Father still today to act as intermediary and advocate for His sheep.
Christ as propitiation
Why do we have Christ as our advocate? Because of the cross. Propitiation is one of those high falutin' theological terms that no one likes, but it is a Biblical word and one that conveys a meaning that I don't think you can get with a different word. It is so vital to understanding the cross. It encapsulates so many ideas: man's sin, God's holiness and justice, the Garden, the atoning sacrifices of the temple, grace. I don't want to do a full study of propitiation here because this is supposed to be more devotional in nature and quite frankly I am not sure I am theologically mature and astute enough to give it a proper treatment. Suffice it to say that at the cross my sin met the holiness of God and was propitiated by grace. The propitiation of the cross shatters all human pride and self-reliance, it destroys the idea of meritorious works in salvation because it exposes the true nature of sin and the white hot wrath of God against that sin, a perfectly just and holy righteous reaction to the rebellion of sin. His death should have been my death, His cross should have been my cross. There was nothing I could do to make God love me more and nothing I can do to make God love me less. An important point that could be overlooked here. When John writes: not for ours only but also for the sins of the whole world, that is not some sort of universalist statement or a defense of man's sovereign free will. Christ died for the sins of the elect in all places and at all times. It was not a limited scope propitiation for just Jews or for just that time period but it also was not a purposeless propitiation. In Christ, at the cross, the sins of all those predestined to salvation were propitiated in full. The cross was infinite in sufficiency but effective only for those ordained from before time began to be saved by grace through the gift of faith. When we examine passages like this, we need to read them in light of the entire Scripture and not imprint our man-centered ideas in place of Biblical doctrines like predestination, election and particular atonement.