In the biblical context, the serpent is always a symbol of evil. However, evil only has as much power as God allows.

Even though man can imitate evil, it is limited by God. God puts an end when he wants.

From the stick of Moses we know that the serpent could only work until Moses took it again. In Exodus 7:15 we see that the same thing happened to Aaron’s stick and the serpent became the stick again.

The message to Pharaoh in Exodus 7:12 and to all who want to understand it is clear: God has the power to set limits. God intervenes when things get too much out of order.