"this solemn command in the presence of God and Christ Jesus." It is implied that God and Jesus will be Paul's witnesses. Alternate translation: "this solemn command having as my witnesses God and Christ Jesus" (See: [[rc://en/ta/man/translate/figs-explicit]])
Here "the living" and "the dead" are used together to mean all people. Alternate translation: "all people who have ever lived" (See: [[rc://en/ta/man/translate/figs-merism]])
Here "kingdom" stands for Christ's rule as king. Alternate translation: "the dead when he returns to rule as king" (See: [[rc://en/ta/man/translate/figs-metonymy]])