In Christian apologetics, the concept of Undesigned Coincidences refers to subtle and incidental agreements between different sources or texts. An undesigned coincidence is said to have occurred when an account of one event in the Bible omits a piece or pieces of information which is filled in, seemingly coincidentally, by a different recording, which helps to answer inquiries raised by the first. According to this approach, undesigned coincidences often occur when one account forgoes a reason for an action which is given by a different account (which often does not mention that action). In this case, so the argument goes, there was a complex unified story both authors are writing down despite gathering data from different witnesses. These coincidences can serve as evidence for the authenticity and reliability of the accounts. In the case of the Gospels, several examples demonstrate such coincidences, supporting the historical veracity of the texts.
Here are simple points that show the Gospels are reliable:
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Matching History: The stories in the Gospels fit well with known historical facts and records, like those by Josephus. These include details about tax collection, feasts, local customs, and rulers' behaviors. Examples, Herod's inquiry about Christ's birth (Mark 6:14-29), the tribute money in Capernaum (Matthew 17:24-27), Joseph's fear of Archelaus (Matthew 2:22).
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Different Views Add Up: Different gospels often provide different angles or additional details on the same event, and when combined, these form a coherent picture. For example, the calling of Peter in Luke 5:1-11 shows an intersecting coincidence where Matthew mentions the mending of the nets (Matthew 4:18-22), while Luke explains the miraculous catch of fish that might have caused the need for mending.
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Small Details Make Sense Together: Sometimes, the connections are not obvious but provide a richer understanding when combined. For example, Mark describes Herod’s birthday feast, and Josephus describes a similar feast made by Herod’s brother, showing a family tradition (Mark 6:21; Antiquities of the Jews, 19.7.1). Or a minor detail of Simon owning a ship for Jesus' use (Luke 5:3).
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Right Places and Customs: The Gospels contain accurate references to geographical locations and cultural practices, such as swine feeding in Gadara, a Grecian city ([Mark 5:1](https://www.bible.com/bible/59/MRK.5.1); Antiquities of the Jews, 17.13.4), or the mentioning of the tax in Capernaum (Matthew 17:24; Antiquities of the Jews 18.10.1).
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People Act the Same: Characters are portrayed consistently across different accounts, such as Martha's practical concerns and Mary's spiritual devotion (John 11:1-44, Luke 10:38-42).
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Real Feelings: Emotional connections and responses are shown in complementary ways. Matthew’s account of Peter’s denial is complemented by Luke’s emotional detail of Jesus' look at Peter, a moment of connection that brings the gravity of Peter's actions into focus (Matthew 26:69-75, Luke 22:61-62).
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Unplanned Alignments: Sometimes the narratives align in ways that are unlikely to have been planned, such as Jesus’ Visit to Jerusalem at Twelve Years Old (Luke 2:42, Antiquities of the Jews 17.15), Jesus’ safety in day but Danger at Night (Matthew 26:5, Luke 22:6) or the change in bystanders' behavior during the crucifixion (Matthew 27:39-44,Mark 15:29-32).
The presence of these undesigned coincidences across the Gospels, and with external historical sources, provides for the reliability and authenticity of these texts. These simple matches across different Gospels and with history show that these coincidences are not the result of fabrication or collusion, but rather reflect accurate re-callings of the events, characters, and teachings of Jesus' life and ministry. They add to the cumulative case for the historical trustworthiness of the Gospels.