What is a parable's purpose in the bible? Are they only meant to teach us moral lessons or something more?

Learn the Purpose a Parable Serves in Scripture

Parables Tell Us How One Thing Is Like Another

Most people assume that Jesus Christ spoke in parables to teach moral lessons. That is not true. The English word parable comes from the Greek word paraboles, which simply means “comparison.” That Greek word is best known for its use in the Scriptures, where it most often refers to the parables of Jesus Christ.

The Truth is, in the time of Christ, the Greek word paraboles was used to refer to any comparison between two things. Therefore, every one of Jesus’ parables is a descriptive comparison put in the form of a brief story that points out how two entirely different things are alike. That is why Jesus began many of His parables by saying, “the kingdom of God is like” this or “the kingdom of heaven may be compared to” that:

Therefore He was saying, “What is the kingdom of God like, and to what shall I compare it? It is like a mustard seed, which a man took and threw into his own garden; and it grew and became a tree; and the birds of the air nested in its branches.” And again He said, “To what shall I compare the kingdom of God? It is like leaven, which a woman took and hid in three pecks of meal, until it was all leavened.”
(Luke 13:18–21) —NASB

The Key to Understanding Parables

The purpose of the parables of Jesus Christ as well as the parables of Moses and all the other Prophets of Israel is to compare the unknown to something that is known. Parables (comparisons) are absolutely essential to an accurate understanding of the Scriptures because they provide the only means by which finite humans existing in a visible physical realm can understand an infinite God Who exists in an invisible spiritual realm. But one must always keep in mind the fact that parables do not depict what some unknown reality actually is; they only describe what it is like, by comparing it to something that is already known.

Understanding the parables of Scripture requires a basic knowledge of two things:

The meaning of each parabolic image (for example, a mustard seed, a tree, leaven, etc.)—that is, what it represents—and
The significance of the comparison being made between those two things—that is, why the comparison is being made.

Believe it or not, the key to understanding the parables of Scripture is found in the Hebrew Scriptures. That’s because every parable of Moses, the Prophets of Israel, and Jesus Christ is based on a parabolic image and a Hebrew idiom whose meaning and significance are explained somewhere in the prophecies of Moses or the other Prophets of Israel.