What does it mean that righteousness is 'upon' all who believe?
It means God's righteousness, not our own, is draped over the believer like a blanket or cloak, totally covering him. This covering is Christ Himself, so when God looks at a believer He sees Christ. It happens by God's work through faith in Jesus Christ, not human effort.
Les explains that the word "upon" pictures being draped with a blanket or cloak that totally covers a person. This is God's righteousness, not our righteousness, which is nothing but filthy rags. It is the righteousness that is by the faith, or faithfulness, of Jesus Christ unto all and upon all that believe. Because of that covering, whenever God looks at the believer, He sees the outer covering, and that covering is Christ. This is what it means to put on Christ: God does not see me or you, but Christ. Les stresses that this happens by a work of God, not by human ability. Just as a person cannot crucify himself, so salvation cannot be accomplished by self-effort. It is done in the area of the invisible, in the Spirit.
Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference: