What does a (solo) personal pronoun express?

It can be used to give emphasis. You can easily emphasize a اِسْم by just adding the corresponding personal pronoun in its normal form after the اِسْم which you want to focus on.

This form is called ضَمِير الْفَصْل – as it separates the subject from the predicate and provides some space in between.

Let us have a look at some examples:

It is Khalid who sits there.

خالِد هُوَ الْجالِسُ هُناكَ.

The engineers were the ones responsible for the success of the project.

كانَ الْمُهَنْدِسُونَ هُم الْمَسْؤُولِينَ عَنْ نَجاحِ الْمَشْرُوعِ.

I have done my duty.

قُمْتُ أَنا بالْواجِبِ.

He wrote the lesson himself.

كَتَبَ هُوَ الدَّرْسَ.