I was discussing the reliability of the New Testament with someone who denies that Paul is a canonical writer. One of his arguments was that 1 Corinthians 4:15 contradicts Matthew 23:9. This is a misunderstanding:

According to D.A. Carson:

Verse 9 moves from “Rabbi” or “Teacher” to “father.” To the best of our knowledge, rabbis were not directly addressed as “fathers.” Some have, therefore, argued that the text is referring to the patriarchs and is saying, “Do not rely on your racial tie to Abraham, Isaac, and Jacob” (cf. 3:9; so J. T. Townsend, “Matthew xxiii. 9,” JTS 12 [1961]: 56–59; Schweizer; and others). Nothing in the context supports this, still less the suggestion that Greek Stoicism stands in the background (van Tilborg, Jewish Leaders, 138). But K. Kohler (“Abba, Father: Title of Spiritual Leader and Saint,” JQR 13 [1900–1901]: 567–80) showed long ago that “the fathers” became a very common way of referring to earlier teachers of the law, especially the great masters (cf. Urbach, Sages, 1:186; 2:906 n. 38; hence the Mishnaic tractate ʾAbot, “The Fathers”). The practice may have stretched back to the days of the prophets (cf. 2 Ki 2:12).

“On earth” does not mean the “fathers” were alive in Jesus’ time but simply contrasts them with the Father in heaven. Their domain is not exalted enough to warrant the latter title. This explains the change from the passive (“do not be called,” vv. 8, 10) to the active (“do not call [i.e., someone else],” v. 9): “do not be called” would be inappropriate since the title was not bestowed until after the teachers of law died and were memorialized. There may be an allusion to Malachi 2:7–10. Like the priests of Malachi’s day whose teaching caused many to stumble, so the revered Jewish fathers have so misinterpreted Scripture that they must not be called “fathers.” There is but one Father, God. Carson, D. A.; Carson, D. A.. Matthew (The Expositor’s Bible Commentary) (Kindle Locations 16597-16609). Zondervan. Kindle Edition.

In essence, Carson explains that Matthew 23:9 is not prohibiting the use of the term “father” in all contexts but is addressing the improper elevation of earthly teachers to a status that rivals the Father in heaven. The term “fathers” here refers to revered teachers of the law, not biological or spiritual fathers in a general sense. This understanding clarifies that there is no contradiction between 1 Corinthians 4:15, where Paul refers to himself as a spiritual father to the Corinthians, and Matthew 23:9.