Paul is emphasizing that he wanted them to have this information. You can translate this double negative in a positive form. Alternate translation: "I want you to know" (See: [[rc://en/ta/man/jit/figs-doublenegatives]])
The word "fruit" is a metaphor that represents people in Rome whom Paul wants to believe the gospel. Alternate translation: "that more people among you might trust in Jesus" (See: [[rc://en/ta/man/jit/figs-metaphor]])