A big misunderstanding
28 And he was angry, and would not go in: therefore came his father out, and intreated him.
29 And he answering said to his father, Lo, these many years do I serve thee, neither transgressed I at any time thy commandment: and yet thou never gavest me a kid, that I might make merry with my friends:
30 But as soon as this thy son was come, which hath devoured thy living with harlots, thou hast killed for him the fatted calf.
31 And he said unto him, Son, thou art ever with me, and all that I have is thine.
32 It was meet that we should make merry, and be glad: for this thy brother was dead, and is alive again; and was lost, and is found.
When a sinner repents and returns to God there is a big celebration. But look at what it says in verse 31 "Son, thou art ever with me, and all that I have is thine". This is in contrast to what is happening with the celebration over the salvation and repentance of the other son.
Yes, when we first come to the Lord we get covered with the best robe, that is the Lord's blood. We get a ring on our finger indicating we are sons of the king. We get our feet shod with the gospel of peace. But we are not "sanctified". That is a process that takes time, it doesn't happen instantly. Nor is it true that "all that God has is ours". It takes time to get the revelation on the various promises of God and to make those promises yours. Nor on day 1 do you have the days and years of fellowship with God.
I was at an event where a brother stood up and shared his testimony of being saved. He was a former felon who used Meth but became desperate, prayed, God answered his prayer and he got saved. Very often it is these testimonies that we celebrate God's salvation and sinners repenting. But I would never trade my fifty years of fellowship with the Lord for that.