«لِيُرَى الْمَعْنَى فِي صُورَتَيْنِ مُخْتَلِفَتَيْنِ»
So that the meaning is apprehended in two different forms.
The listener first grasps an unspecified conception and later sees the precise content. These are two cognitive encounters with one intended meaning. This layered apprehension can be more effective than a single, wholly immediate presentation.
The effect is not created by communicating two unrelated facts. It is the deliberate movement from initial awareness to exact understanding. Replacing a word with a synonym without a new purpose would not achieve the same rhetorical benefit.