هِيَ النَّفْسُ مَا حَمَّلْتَهَا تَتَحَمَّلُ
It is the soul: whatever burden you place upon it, it bears.
A pronoun at the start may indicate an affair or situation that the following clause will explain, rather than refer back to an earlier noun. This creates anticipation before the fuller statement arrives.
هُوَ اللَّهُ أَحَدٌ
He—Allah is One.
A pronoun of affair must not be confused indiscriminately with every ordinary referential pronoun. The following clause supplies its interpretive content.