The phrase "this letter is from" is implied. AT: "This letter is from James, a servant of God and of the Lord Jesus Christ" (See: [[rc://en/ta/man/translate/figs-explicit]])
Possible meanings are 1) this is a synecdoche for Jewish Christians, or 2) this is a metaphor for all Christians. AT: "to God's faithful people" (See: [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-metaphor]])
The term "dispersion" normally referred to the Jews who were scattered in other countries, away from their homeland Israel. This abstract noun can be expressed with a phrase with the verb "scattered." AT: "who are scattered around the world" or "who live in other countries" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
The expressions "the testing," "your faith," and "endurance" are nouns that stand for actions. God does the testing, that is, he finds out how much the believers trust and obey him. Believers ("you") believe in him and endure suffering. AT: "when you suffer hardships, God is finding out how much you trust him. As a result, you will become able to endure even more hardships" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])