The Flame can be strengthened at the Flame Altar. This empowers you to pierce the Shroud further, and to construct more bases to protect Embervale from its reach. In order to strengthen the Flame, Sparks and other materials are needed. Find Sparks in Flame Sanctums and Flame Shrines.

You've obtained a Spark. Use the Spark to strengthen the Flame at your Flame Altar. Strengthen the Flame at the Flame Altar to increase your Shroud Passage Level and to establish more bases.