A snare is a trap to catch some prey, but more often refers metaphorically to entrapping people. The ephod Gideon made was soon an object of idolatrous worship for the Israelites including his family. Praise and worship for the created, instead of the Creator (with or without our knowledge) constitutes sin and God hates idolatry. If we are walking closely/alertly with Christ and constantly seeking spiritual guidance from the Holy Spirit, we are not likely to sin in ignorance.
The Israelites sinned by worshipping and serving the ephod instead of the true God. Their act of abandoning God is the essence of their sin. Gideon was wrong to build the ephod because it represented a source of unfaithfulness, i.e., idolatry. How like his father he has become, instead of Baal, the source of sin is the ephod.
It seems no matter how much love and protection and deliverance God showed those who love Him, we still wander off seeking the things that God hates. Lord, please keep me aware of Your lighted pathway and stop me from straying.