Harmony of the gospels — shows consistency in all four texts written by different authors at different times in different locations — led by the Holy Spirit!
The synoptic gospels, Matthew, Mark and Luke overlap a lot, covering much of the same material, and they are in harmony.
Written by different authors in different places and at different times and they agree about what was said.
And where John’s gospel overlaps, it agrees too. [John’s gospel mostly covered different discussions, but also seamlessly overlapped a number of times, covering the same material.]
All four gospels in harmony confirm that we can trust we are reading what Jesus really said.
The Holy Spirit made sure this would happen, inspiring the authors, etc..
Books, often called “harmony of the gospels” show this consistency by placing the same texts from the different gospels side by side, so they can be compared.
Here is an excellent one online. See for yourself:
The Synoptic Gospels presented side-by-side