The fatted calf is symbolic of the need for mercy. .
The son when he returned did not get what he deserved.
The Law says he was to be stoned.
Deu. 21 18 If a man has a stubborn and rebellious son who does not obey his father and mother and will not listen to them when they discipline him, 19 his father and mother shall take hold of him and bring him to the elders at the gate of his town. 20 They shall say to the elders, “This son of ours is stubborn and rebellious. He will not obey us. He is a profligate and a drunkard.” 21 Then all the men of his town shall stone him to death. You must purge the evil from among you. All Israel will hear of it and be afraid. NIV
The fatted calf becomes the sacrifice offered for his sin. (the crucifixion)
23 And bring hither the fatted calf, and kill it;
We are not saved by God’s love; God loves the whole world, and the whole world is not saved. We are saved by God’s grace, and grace is love that pays a price. Because of the cross the Father has given grace and mercy.
Eph 2 As for you, you were dead in your transgressions and sins, 2 in which you used to live when you followed the ways of this world and of the ruler of the kingdom of the air, the spirit who is now at work in those who are disobedient. 3 All of us also lived among them at one time, gratifying the cravings of our sinful nature and following its desires and thoughts. Like the rest, we were by nature objects of wrath. 4 But because of his great love for us, God, who is rich in mercy, 5 made us alive with Christ even when we were dead in transgressions—it is by grace you have been saved. 6 And God raised us up with Christ and seated us with him in the heavenly realms in Christ Jesus, 7 in order that in the coming ages he might show the incomparable riches of his grace, expressed in his kindness to us in Christ Jesus. 8 For it is by grace you have been saved, through faith—and this not from yourselves, it is the gift of God— 9 not by works, so that no one can boast. NIV
What a picture of what Jesus did for us on the cross!