Reducing sauce with chicken or other meat is the secret behind producing a glaze. Reducing the sauce over heat evaporates most of the water, and the volume of the sauce reduces, making it thick. It also caramelizes the sugar in it, honey, in this case, thus making it look glazy. Such reductions are often made at the end, when the chicken is almost but not entirely cooked. Keeping it too long over heat might burn the sauce and make it taste bitter.