Advertisers promise salvation from all sorts of conditions that their product will repair. Politicians promise salvation from poverty etc. Paul and Silas were in jail. Maximum security with their feet in stocks. But there came a violent earthquake and the jail was thrown open and the chains broken.
Salvation is about freedom.
Salvation is freedom from sin. It is a common condition throughout the world. All of man's efforts to eradicate it have failed. The jailer, though free, was imprisoned, enslaved to sin. Yet those who were in prison, were truly free.