1.  Who is doing the binding and unbinding?

In Matt 16:19 it is either Peter alone or “disciples” as in v. 13, 20

In Matt 18, it is either a) disciples as in v. 1 or quite likely b) believers in the first century and future generations. One would be hard pressed to say “apostles” only on verse 18 when they would say all generations of believers in the surrounding verses of 15, 16, 17, 19, and 20.

 2. What bindings are temporary and which are permanent?

It seems that we have been quite comfortable loosing the acts of foot washing and head covering and holy kiss greetings as temporary forms reflecting permanent principles of service, humility, and brotherly affection.

 I believe that the apostles had the wisdom of a few enlightened parents who realized (perhaps too late) that more rules lead to greater demand for discipline. I read between the lines in Acts 15:19 that the apostles and elders had no interest in requiring more of the Gentiles than what fellowship with Jews would demand. (I now take v 21 to mean that there is a Jewish community in “every city” thus creating a possible split between Gentiles and Jews over the most egregious violations of the law of Moses.) The sanctions on idol meat and blood were based on the principle of brotherly consideration; the sanction on sexual immorality is based on holiness and the spiritual bonding aspect of intercourse.