أَنَا رَجَوْتُكَ فِي هٰذَا الْأَمْرِ، وَأَنْتَ وَعَدْتَنِي بِإِنْجَازِهِ
I relied on you in this matter, and you promised me to complete it.
A pronoun works when the speaker, hearer, or absent referent is identifiable from the speech situation. First-person, second-person, and third-person pronouns often avoid needlessly repeating a full name.
In the example, the identities of the two participants are already supplied by the act of addressing one another. Pronouns provide economy and precision, as long as the referent is recoverable from context.