A "lamb" is a young sheep. Here is it used symbolically to refer to Christ. See how you translated this in [Revelation 5:6](../05/06.md). (See: [[rc://en/ta/man/jit/writing-symlanguage]])
This refers to one group of people. The words "called" and "chosen" can be expressed in active form. Alternate translation: "the ones whom God has called and chosen, who are faithful to him" (See: [[rc://en/ta/man/jit/figs-activepassive]])