The First Gateway opens by selecting a particular pane of glass in each of the stained glass windows in a specific order, within a short time limit.
The first pane of glass that needs to be selected will be flashing green in the large window on the lower left part of the Seventh House menu screen. The specific panes of glass that need to be clicked in each of the other windows can be determined by opening those puzzles and analyzing the flashing stained glass windows. The pane that needs to be clicked will be flashing bright green.
Once you have determined the 7 panes that need to be selected, quickly click each of them in the proper order on the Seventh House screen. The order corresponds to the titles of each window's puzzle (The First Delivery, The Second Delivery, and so on...).