The Apostles were being persecuted by the Religious Leaders for preaching the Gospel Message.  They had been brought before them to be condemned to death when a Teacher of the Law by the name of Gamaliel tried to talk  some sense into them.  In these verses you’ll find the word “if”  twice.  One word with two completely different meanings.  “If it’s the work of men…”  Here Gamaliel thought there was only a slight possibility that it was true and the Apostles were acting on their own.  “But if it’s from God…”  Here the if Gamaliel used meant he firmly believed it was from God and nothing the Religious Leaders did would stop it.  That’s why he urged them to just walk away…for he knew they didn’t have the capacity or power to destroy a work of God.