A flare is a bright burst of flame where your candle suddenly gets hotter and/or brighter with a very tall and enthusiastic flame. The longer it is sustained, the stronger the sign.
This means that someone else has the same goal you do. Someone else is already doing work or praying for the same or a compatible goal, and their energy is helping your work succeed.
This often shows up if you have had someone else do spell work for the same goal already, or if you and someone else are deliberately working as a team.
What To Do:
There's no need to do anything but you might want to ask around and/or get a reading to confirm where this energy comes from. You may have an ally that you can connect with to build better results in the future.