With revelation comes responsibility. That which God has revealed to us, belong to us so that we may do, that is, apply the truths that God has revealed. There are secrets that God has not revealed and some secrets that God has revealed to only some, but not to everyone.

In the Old Testament, the Hebrew word for "mystery" or "secret" occurs in the book of Daniel in 2:18, 19, 27, 28, 29, 30, 47; 4:9. It relates specifically to God's revelation through Daniel of dreams and visions whose meanings were hidden to others.

The New Testament word is "mysterion." It occurs twenty-seven times in the New Testament, twenty of them in Paul's writings (Romans 11:25; 16:25; 1 Corinthians 2:7; 4:1; 13:2; 14:2; 15:51; Ephesians 1:9; 3:3, 4, 9; 5:32; 6:19; Colossians 1:26, 27; 2:2; 4:3; 2 Thessalonians 2:7; 1 Timothy 3:9, 16). It's used seven times (Matthew 13:11; Mark 4:11; Luke 8:10; Revelation 1:20; 10:7; 17:5, 7) in connection with parables about God's kingdom or truths disclosed in the Book of Revelation. The word is always associated with a verb of revelation or proclamation. A "mystery" is an insight into some present-day Christian experience or future expectation not unveiled clearly in the Old Testament.

In the Vine's Expository Dictionary of New Testament Words, under the words "mystery" and "secrets", the meaning is something hidden, and which being outside the range of unassisted natural apprehension, can be made known only by divine revelation, and is made known in a manner and at a time appointed by God, and to those only who are illumined by His Spirit. In the ordinary sense a "mystery" implies knowledge withheld; its Scriptural significance is truth revealed. Hence the terms especially associated with the subject are "made known," "manifested," "revealed," "preached," "understand," "dispensation." The definition given above may be best illustrated by the following passage: "the mystery which hath been hid from all ages and generations: but now hath it been manifested to His saints" (Colossians 1:26 RV). It is used of spiritual truth generally...

I had always thought that a parable clarified the spiritual by bringing into the physical an illustration of spiritual truth. What I learned is that a parable keeps the spiritual truth as a secret or mystery. For instance:
Regardless of what we think, God does not share secrets with his enemies (1 Corinthians 2:7‑8), God only shares secrets with His friends (Genesis 18:16‑19).

When Jesus was belittled for his Messianic claims, for instance in John 7:41‑43,
Jesus could have cleared this up by saying, I was born in Bethlehem, but raised in Nazareth as prophecy predicted. But He left his enemies and the unbelieving world to continue in their falsehoods because they had no love of the truth, so they believed a lie.
But to those who follow Christ, embrace His words, apply His words, do His words (Matthew 7:24), He will explain everything.
Do you love the truth? Will you follow the truth wherever it may led? If it led you into an unpopular position or unpopular group, would you accept the persecution (Romans 8:17) and follow the One who is truth (John 14:6)? Selah! Think about that!