Israelites, can at best be equated to the present day believers. They are a chosen nation. We understand their record better if we put ourselves in their place. The elder son, in the 15th Chapter of Luke and the younger in Matt 21 : 30, both are God's people. The first one, in the first parable had always been with the father. The second one, in the second parable also goes to the kingdom of heaven. But a bit late.
What's the difference? With whom the father is pleased, makes all the difference. The repentant one makes God happy. In your eyes you are not like the two boys who needed repentance. You think you are better than they are. So you keep them away. You treat them as people you don't want to identify with.
Please notice that the Lord, all along kept only one group of people away. The hypocrites! The two parables are in such context. How are some groups, who call themselves believers, behaving? Where does their teaching take the members to? Are they not making the members ignorant of the heart of the Father and the Son and the Spirit?
High time that the whole counsel of God had reached them! Other persons in the Churches who you come accross may not be unbelievers. They may be better placed than you are. Wake up brothers and sisters. If they are wanting in sound doctrine help them. Their conduct? Yes, but wait. Your job?Help it is (Gal 6 : 1; Jude 22 and 23 and Daniel 12 : 3).There is nothing like grading in sins, the earlier we realise the better it would be.The closer we go to God's word the more sensitive we become to our sins.
Let us get rid of those sins by confessing and seeking forgiveness.The Spirit of His son is in us to help us through. It is only the believers who know what sin is, not unbelievers!