God giving people skills and work to do and guiding the events of their lives is spoken of as if he were dividing physical objects and giving parts out to them. Alternate translation: "as the Lord has assigned each one his life"
The word "walk" is a metaphor for "live." Possible meanings of the word "called" are 1) it refers to people responding to the gospel. Alternate translation: "each one should live as he was when he became a Christian." Or 2) it is a metaphor for "commanded" or "instructed." Alternate translation: "each one should live as God has instructed him to" or "each one should follow God's commands as he lives his life"