Hebrews 2:3-4

3How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him; 4God also bearing them witness, both with signs and wonders, and with divers miracles, and gifts of the Holy Ghost, according to his own will?

Comment: The author reminds his audience that the message concerning Jesus' death and resurrection was accompanied by various supernatural signs [cf. Mark 16:20]. Apparently they had personally witnessed miracles by those who preached the message of salvation through Jesus. Otherwise, why would the author be reminding his audience of things they weren't familiar with as the basis for an exhortation to remain faithful? As the author points out, supernatural signs accompanying the message would certainly be compelling evidence for the truth of that message.