The ESV translation of 1 John 4:10 uses the word ‘propitiation’, a big scary theological term which has dropped out of common use in English as some Bible translators decided that we are too stupid or lazy to work out what it means.
The word ‘propitious’ means to have a favourable disposition towards someone. In ancient Greek mythology it was assumed that the gods were generally ill-disposed towards humans so had to be placated, bribed and appeased to make them happy. However, this idea of changing God’s attitude toward us is not how propitiation is used in the Bible. We cannot give anything to God or do anything for Him that would change His attitude towards us, it all comes from God (Job 41:11).
It is Jesus Christ who in himself, by his death became the personal means through whom God shows mercy to us sinners who believe in Christ. (Vine’s Expository Dictionary, p494)
Sin is an offence against God for which there is a penalty… death (Romans 6:23). Only a sinless person could pay the penalty for sin, and that would mean dying. Therefore no human can atone for their own sin. God has provided a substitute for us, the man Jesus Christ lived a sinless life so is able to pay the penalty (1 Timothy 2:5). Jesus is also the Son of God and so could bear the sin of all humanity in himself, thus paying for the sins of all people in the one perfect sacrifice (Hebrews 10:12-14).
Propitiation is the work that God initiated and completed to enable us to have fellowship with Him.
For a passionate insight about what propitiation means for us check out C.J. Mahaney’s message on Jesus Christ as the Mediator.