Complex sentence: The effect is also caused by the wound Frodo receives from the Morgul Blade-this wound is an attempt to transform him into a wraith and allows him to see the shadow world more clearly, including seeing Glorfindel as he appears "on the other side".
Split into simpler sentences: The effect is also caused by the wound Frodo receives from the Morgul Blade. This wound is an attempt to transform him into a wraith and allows him to see the shadow world more clearly, including seeing Glorfindel as he appears "on the other side".