Jesus taught by means of parables, and they came in threes in order to emphasise the point or principle Jesus was making.
At a basic level, a parable is a short story designed to convey a concept to be understood and/or a principle to be put into practice. This, however, tells us more about the intent of a parable than what it actually is. The word “parable” in Greek literally means, “to set beside,” as in the English word “comparison” or “similitude.” In the Jewish culture, things were explained not in terms of statistics or definitions as they are in English-speaking cultures. In the Jewish culture of biblical times, things were explained in word pictures.
In the first two parables, Jesus uses every-day or common situations to represent a spiritual point. The sheep, the coins and the prodigal son are not real events – they are allegorical.
The lost sheep parable illustrates how the shepherd has compassion for the one that went astray and would be in danger of injury or death unless it was found and returned to the fold. The shepherd also has responsibility for every single sheep under his care. If a sheep is lost to wolves or becomes injured then it is the shepherd who has to make recompense to the owner of the flock. The spiritual point is that Jesus, as the good shepherd, has vowed that he will never lose any one of the “flock” entrusted to him by his heavenly father. We can trust Him for our eternal security.
In the “lost coin” parable, the ten silver coins refer to a piece of jewellery with ten silver coins on it worn by brides. This was the equivalent of a wedding ring in modern times.
Imagine the distress of the woman who has lost one of those coins. Perhaps it fell out and she was unable to find it, so she literally turns her house upside down and inside out to locate it – probably before her husband comes home and asks her why one of those valuable coins is missing.
The sheep wandered off. The wife discovered one of those coins had fallen out of her necklace. The prodigal son decided to clear off and do his own thing. The cause of the loss is immaterial. This is a parable, not a real event.
The point is spiritual. God cares for each and every one of us and regardless of how we go astray or “get lost” spiritually speaking He is there to draw us back into the safety of His bosom. We can trust the shepherd, Jesus, who searches for the one lost sheep. We can trust our heavenly father who welcomes back wayward sons (and daughters) with open arms. We can trust God in all things because he cares for us.
Check out the article below which makes a powerful point with regard to the background of these three parables. Jesus was sending a strong message to the hypocritical and self-righteous Pharisees.
The presupposition behind the statement of the Pharisees, “this man welcomes sinners,” is what Jesus addresses in all three parables.
https://www.gotquestions.org/parable-lost-sheep-coin.html