Because all of them have sinned and were deprived of the glory of God. And they are justified by grace without charge and by the redemption that is in Jesus The Messiah. (Romans 5:23, 24)
The "they" in v. 24 are the "all" of v.23. We know all mankind have sinned. Verse 24 then says that all mankind are justified by what Jesus did. Praise God through Jesus for being the Savior of the World!!!