"So my advice is, leave these men alone. Let them go. If they are planning and doing these things merely on their own, it will soon be overthrown. But if it is from God, you will not be able to overthrow them. You may even find yourselves fighting against God!" (Acts 5:38, 39 NLT)
You cannot stop the work of God no matter how much you oppose it. Gamaliel was wise to recognize this and to advise his colleagues to avoid further action lest they actually "[fight] against God." The devil has been trying to thwart the work of God ever since the beginning of time, but he will never succeed. God will accomplish His purposes no matter who resists Him and He'll even use their foolishness to bring His will to pass. God always prevails!