"I have written about the true grace of God." Here the word "grace" refers to the gospel message, which tells of the kind things that God has done for believers. (See: [[rc://en/ta/man/translate/figs-metonymy]])
The word "it" refers to "the true grace of God." Being strongly committed to this grace is spoken of as standing firmly in one place, refusing to move. AT: "Remain strongly committed to it" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "The woman" probably refers to the group of believers who live in "Babylon." Possible meanings for "Babylon" are 1) it is a symbol for the city of Rome, 2) it is a symbol for anywhere that Christians are suffering, or 3) it refers literally to the city of Babylon. It most likely refers to the city of Rome. (See: [[rc://en/ta/man/translate/writing-symlanguage]])
Peter speaks of Mark as if he is his spiritual son. AT: "my spiritual son" or "who is like a son to me" (See: [[rc://en/ta/man/translate/figs-metaphor]])