According to Vine's Expository Dictionary:
Propitiation:
[ B-2,Noun,G2434, hilasmos ]
akin to hileos ("merciful, propitious"), signifies "an expiation, a means whereby sin is covered and remitted." It is used in the NT of Christ Himself as "the propitiation," in 1Jo 2:2; 4:10, signifying that He Himself, through the expiatory sacrifice of His Death, is the Personal means by whom God shows mercy to the sinner who believes on Christ as the One thus provided. In the former passage He is described as "the propitiation for our sins; and not for ours only, but also for the whole world." The italicized addition in the AV, "the sins of," gives a wrong interpretation. What is indicated is that provision is made for the whole world, so that no one is, by Divine predetermination, excluded from the scope of God's mercy; the efficacy of the "propitiation," however, is made actual for those who believe. In 1Jo 4:10, the fact that God "sent His Son to be the propitiation for our sins," is shown to be the great expression of God's love toward man, and the reason why Christians should love one another.
Christ's death was not a "propitiation Godward" (i.e. from man to God).
Again, from Vines:
It is used in the NT of Christ Himself as "the propitiation," in 1Jo 2:2; 4:10, signifying that He Himself, through the expiatory sacrifice of His Death, is the Personal means by whom God shows mercy to the sinner who believes on Christ as the One thus provided.
Nor is Christ's death limited to those you have decided He died for.
1 John 2:2 And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world (1 John 2:2).
Again, from Vines:
What is indicated is that provision is made for the whole world, so that no one is, by Divine predetermination, excluded from the scope of God's mercy; the efficacy of the "propitiation," however, is made actual for those who believe.
When God says the whole world, God means the whole world.
The Lord Jesus Christ gave Himself for the whole world. In offering Himself as a sacrifice, His life was sufficient to cover every single person who has ever been born ... from time of Adam to now to future born children.
That is the value of His sacrifice.