That is more likely that they will give testimony according to its [true] objective, or [at least] they would fear that [other] oaths might be taken after their oaths. And fear Allah and listen; and Allah does not guide the defiantly disobedient people.
English Transliteration
Thalika adna an yatoo bialshshahadati AAala wajhiha aw yakhafoo an turadda aymanun baAAda aymanihim waittaqoo Allaha waismaAAoo waAllahu la yahdee alqawma alfasiqeena
Tafsir of Verse 108
So it is likelier that they will bear testimony in proper form, or else they will be afraid that after their oaths, oaths may be rebutted. Fear God, and hearken; God guides not the people of the ungodly.
That is most suitable: that they may give the evidence in its true nature and shape, or else they would fear that other oaths would be taken after their oaths. But fear Allah, and listen (to His counsel): for Allah guideth not a rebellious people: