God, in his providence, designed all the events of the first century Church so that various crises came up in churches when apostles couldn't get there soon enough, or in person. So they wrote letters.
We live in an age where believers are already justified through our union with Christ, but not yet fully restored as promised in the New Covenant. In Ephesians 2:1-10, Paul points out that we are given a taste of the New Age yet to come.
Jesus Christ as the servent-leader.
When courtesy becomes cruelty.
Should we demur from God-given revelation when Scripture identifies Jesus as the fulfillment of Israel? Jesus is the true Israel of God.