1. In earliest Christian antiquity Paul was understood to have ascended to the 'third heaven' and then Paradise which Church Fathers insinuate was in the 'eighth' heaven (i.e. above the seventh)
2. there was a gospel called for some reason 'the Diatessaron'
I don't think that a gospel made up of four gospels (as 'Diatessaron' is commonly interpreted) would be called 'the Diatessaron.' I have always thought it had something to do with musical theory (where the terminology originates).
Curiously if we imagine Paul standing at ground zero ('C' in musical terms), D would be the 'first heaven' and E would be the 'second heaven.' That means F was the 'third heaven.' G = fourth, A = fifth, B = sixth heaven, C = seventh heaven. In essence then C was both the seventh heaven and an octave which spanned earth to the highest heaven.
But Paul's journey from 'earth' or C to 'third heaven' or F and finally Paradise in the seventh and highest heaven has musical theoretical implications. The journey from C to F was a 'Diatessaron'
In classical music from Western culture, a fourth is a musical interval encompassing four staff positions (see Interval number for more details), and the perfect fourth (About this sound Play (help·info)) is a fourth spanning five semitones (half steps, or half tones). For example, the ascending interval from C to the next F is a perfect fourth, as the note F lies five semitones above C, and there are four staff positions from C to F. Diminished and augmented fourths span the same number of staff positions, but consist of a different number of semitones (four and six).
The perfect fourth may be derived from the harmonic series as the interval between the third and fourth harmonics. The term perfect identifies this interval as belonging to the group of perfect intervals, so called because they are neither major nor minor (unlike thirds, which are either minor or major) but perfect.
Up until the late 19th century, the perfect fourth was often called by its Greek name, diatessaron.[1] Its most common occurrence is between the fifth and upper root of all major and minor triads and their extensions.