The eldest son
There is many facets to the eldest son that can be addressed here as he is a reflection of those that have been loyal to God all the time. The religious leaders that were here listening to Jesus tell this parable is one facet. Those within churches that see people come into their churches that look and act different then they do. These are just two facets.
The religious leaders saw Jesus Christ as a threat to their command of the Israeli people. Thus their anger and hatred toward Him. The fact that Christ was causing people to come to God as they never did with those in religious power. That sinners would go to Him and then leave from Him no longer sinning thus becoming the younger son. Being dead and now alive once again. The religious leaders in their own minds saw themselves as being loyal to God, even though there was mounting evidence that this was the furthest thing from the truth.
In many churches today people form a group and see those that come into their churches as invaders. So they make it hard for these intruders to fit in or grow in their belief in Jesus Christ and His Father.
These are all aspects of the eldest son.
What the father says is clear and to the point.
Luke 15:31 – “His father said to him, ‘Look, dear son, you have always stayed by me, and everything I have is yours. 32 We had to celebrate this happy day. For your brother was dead and has come back to life! He was lost, but now he is found!’”
Simply there is no need to be jealous or envious. For you are a part of the body of Christ, and when someone comes to realize that truth. That God is the Creator of ALL. That they have come home through accepting Jesus as their Savior is a time of joy and celebration. For they were dead and now they are alive and will for all eternity.
This is something that is open to all that are willing to see the truth. Be they now Atheist, Muslim, Buddhist, or even think they are Christian. All they need do is not live their lives in the here and the now, but to look to the eternal life that is yet to come. To stop living in the temporal and plan to exist for billions upon billions of years in the embrace of God, through His Son Jesus Christ our Savior.