Through this move, White lines up 3 of his pieces on the c7-i3 line and closes the c1-i3 line at the same time. Black must play 1. … a3-d6;x.
White, by means of 2. d1-d7, pushes Black’s last GIPF in a blocked position. where it cannot be defended with one single move. Whatever Black plays, White will always be able to occupy h4 with his next move and capture Gd7.