This expression means "Christ willingly gave his life for us" or "Christ willingly died for us" (See: rc://en/ta/man/translate/figs-idiom)
material possessions like money, food, or clothing
"realizes a fellow believer needs help"
"Heart" here is a metonym for "thoughts and intentions." AT: "and does not show him compassion" or "and does not willingly help him" (See: rc://en/ta/man/translate/figs-metonymy).
John uses a question to teach his audience. AT: "God's love is not in him" (See: rc://en/ta/man/translate/figs-rquestion)
John was an elderly man and their leader. He used this expression to show his love for them. See how you translated this in 1 John 2:1. AT: "My dear children in Christ" or "You who are as dear to me as my own children" (See: rc://en/ta/man/translate/figs-metaphor)
The phrases "in word" and "in tongue" both refer to what a person says. The word "love" is understood in the second part of the sentence. AT: "do not just say that you love people, but show that you truly love people by helping them" (See: rc://en/ta/man/translate/figs-doublet and rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-ellipsis)