A sermon? Bring an extra hard drive...
If you are on Windows 32 bit or using a drive formatted for FAT32 the maximum file size (for each track) is 4GB. As mentioned, Reaper will create additional files as needed if you pass the size limit. For other operating systems the max file size is large enough you won't have to worry about it.
Depending on the recording format you use, recording time is figured this way.
Mono track at 44.1 KHz sample rate, 24 bit word size:
4 GB = 4,294,967,296
4 GB / 24 bit / 44100 words per sec = 4057 sec
or roughly 1.1 hour
Stereo track will cut that time in half.