Psalm 138

Though I walk in the midst of trouble,
you preserve me against the wrath of my enemies;
you stretch out your hand,
and your right hand delivers me.
The Lord will fulfil his purpose for me;
your steadfast love, O Lord, endures for ever.
Do not forsake the work of your hands.

Above the Hebrew בְּעַד - b'ad - is translated as purpose.

This transforms a preposition into an object, and an abstract object at that.

The preposition is generally used to indicate where or how action occurs.

A very literal translation of the verse: That Which Exists is completed through, behind, about, on behalf of.

God's purpose is fulfilled, sometimes indirectly, sometimes even by sinners, sometimes even by me.

Psalm 138