Biblical Answer

Step 1: Define Sexual Immorality

Sexual immorality is a broad term that encompasses various forms of illicit sex, including pre-marital unchastity, incest, post-marital immorality, and homosexual activity. In the context of Matthew 19, sexual immorality is primarily a reference to literal sexual immorality, but it may also draw on Old Testament sexual metaphors for idolatry and unfaithfulness to God.

Step 2: Identify the Specific Context of Matthew 19

In Matthew 19, Jesus is discussing the topic of divorce and remarriage. The Pharisees ask Jesus about the grounds for divorce, and Jesus responds by citing Genesis 2:24 and stating that divorce is only permissible in cases of sexual immorality. The context suggests that Jesus is prohibiting remarriage after divorce, and the term "sexual immorality" is likely referring to literal sexual immorality, such as adultery or fornication.

Step 3: Analyze the Meaning of Sexual Immorality in Matthew 19

Given the context of Matthew 19, it is likely that Jesus is using the term "sexual immorality" to refer to any form of illicit sex, including pre-marital unchastity, incest, or post-marital immorality. The emphasis on sexual fidelity before marriage and the prohibition against remarriage after divorce suggest that Jesus is upholding the importance of sexual purity and fidelity in marriage.

The final answer is: $\boxed{Literal sexual immorality, including pre-marital unchastity, incest, or post-marital immorality.}$