We call our priests, "Father." But Jesus teaches in the Bible that we must call no man on earth "father" (Matt 23:9). How can I explain why we Catholics use this term for priests?

If the purpose of Jesus were to banish the use of the word “father” in reference to human males, then it would seem the other New Testament authors never got the memo. In the New Testament alone there are 195 uses of the word "father(s)" to refer to earthly human males. Hence, it seems clear that to understand our Lord's word as an absolute banishment of the term for any but God is not supported by the practice evident in Scripture itself.

The Catholic practice of calling priests “Father” has several meanings.

In one sense it is meant as an affectionate family term. Parishes are like a family and use family terms such as "brother," and "sister" for men and women religious, "mother" for the superior of a group of religious sisters, and "father" for priests.

Priests imitate biological fathers in a spiritual way. Just as fathers give life, food, encouragement and instruction, so priests give us these things in the spiritual order. They confer spiritual life by God's power at the baptismal font, give food through the Eucharist, and meet other spiritual needs through the other sacraments and by instruction and encouragement.

Thus, by analogy, we call priests "father." St. Paul referred to himself as a father: "...you have many guides but not many fathers, for I became your father in Christ Jesus through the Gospel (1 Cor 4:15). For you know how, like a father with his children we exhorted and charged each one of you to lead a life worthy of God (1 Thess 2:10). Timothy...as a son with a father has served me in the gospel. (Phil 2:22)

We can see how calling priests "father," in this sense, is not against Biblical principles. St. Paul himself makes use of the term in this way.

In saying “Call no one on earth your Father” Jesus is emphasizing that God is pre-eminent. No earthly father, biological or spiritual, can ever over-rule or take the place of the heavenly Father. God is ultimately the Father of all fathers, and we can never call any man "father" like we call God, "Father."