How does the selection of what's MANDATORY work?
You wrote:
“How does the selection of what’s MANDATORY work?”
I’ll simply answer your question with a question since you ignored the rest of my response: Who decided on the canon of scripture and why are you obligated to follow that decision?
“How does the selection of what’s MANDATORY work?”
Well, to start with, you read the entire Bible. You offer communal living and tithing as your examples. Communal living was practiced by the church for a time in Jerusalem, but not elsewhere - and other versus such as 2 Thess 3 say,
“6 Now we command you, brothers, in the name of our Lord Jesus Christ, that you keep away from any brother who is walking in idleness and not in accord with the tradition that you received from us. 7 For you yourselves know how you ought to imitate us, because we were not idle when we were with you, 8 nor did we eat anyone’s bread without paying for it, but with toil and labor we worked night and day, that we might not be a burden to any of you. 9 It was not because we do not have that right, but to give you in ourselves an example to imitate. 10 For even when we were with you, we would give you this command: If anyone is not willing to work, let him not eat. 11 For we hear that some among you walk in idleness, not busy at work, but busybodies. 12 Now such persons we command and encourage in the Lord Jesus Christ to do their work quietly and to earn their own living.”
For tithing, 2 Corinthians 9: “ 6 The point is this: whoever sows sparingly will also reap sparingly, and whoever sows bountifully will also reap bountifully. 7 Each one must give as he has decided in his heart, not reluctantly or under compulsion, for God loves a cheerful giver. 8 And God is able to make all grace abound to you, so that having all sufficiency in all things at all times, you may abound in every good work. 9 As it is written, “He has distributed freely, he has given to the poor; his righteousness endures forever.”
Most of the Christians I know use 10% as a good rule of thumb for a starting point, but most also give more than that - if not to the church, then to charity.
If something is mandatory, it is usually obvious.
“16 For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life. 17 For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. 18 Whoever believes in him is not condemned, but whoever does not believe is condemned already, because he has not believed in the name of the only Son of God.”