 It was the topic of a highly political controversy in the early 1930s and was condemned as heretical 
in 1935.John Maximovitch in "The Orthodox Veneration of the Mother of God", discusses at length why the sophianism of Sergius Bulgakov is heresy, attempting the deification of the Theotokos.Vladimir Lossky likewise rejects the teachings of Solovyev and Bulgakov.