for an angel of the Lord went down at certain seasons into the pool and stirred up the water; whoever then first, after the stirring up of the water, stepped in was made well from whatever disease with which he was afflicted. John 5:4 NASB
Here it was necessary to move to the NASB as the NIV and some other Bible versions omit this verse.
It is not that those lying around the pool were able to see an angel stirring the water. They watched for any agitation therein and assumed that when it occurred the water then possessed a healing power which would remove the infirmity of the initial person into the pool.
God works in many different ways, sometimes directly, sometimes through His angels, and other times through others among us. How has God healed you? Do you allow Christ to utilize you as His vessel in the healing of others? Be His vessel, allowing Him to use you as one of His healing instruments.