How To: Programmatically display selected features in ArcMap
If you are using VBA to select features in ArcMap, the code in this article will allow you to display those features.
Use IFeatureSelection::SelectionSet on your selection set.
Dim pFSelection as IFeatureSelection
Set pFSelection = pFeatureLayer
Set pFSelection.SelectionSet = MySelectionSet
Dim pAV As IActiveView
Set pAV = pDoc.FocusMap
pAV.ScreenDisplay.Invalidate Nothing, True, pAV.ScreenCacheID(esriViewGeoSelection, Nothing)