The Lord is giving one command in two different ways to emphasize that Paul should certainly continue preaching. AT: "You must not be afraid and, instead, continue to speak and not become silent" (See: [[rc://en/ta/man/translate/figs-parallelism]])
The Lord gives the same command in two different ways to strongly command Paul to speak. AT: "you must certainly continue to speak" (See: [[rc://en/ta/man/translate/figs-doublet]])
It can be stated explicitly what the Lord wants Paul to speak. AT: "do not stop speaking about the gospel" (See: [[rc://en/ta/man/translate/figs-explicit]])