This Apostle wrote to contend for the true faith. Who is he?

John wrote 3 epistles. He also wrote the Gospel of John and Revelation. .

Source:

1^st John, 2^nd John, 3^rd John

This letter clarified the relationship between faith and works also other aspects of Christian conduct. Who wrote this important letter?

This is the Epistle of James. This is a general Epistle addressed to the twelve tribes scattered abroad.

Source:

James

Which churches received two letters from Paul in the New Testament?

The Church at Corinth, 1^st and 2^nd Corinthians. Also the church at Thessalonika, 1^st and 2^nd Thessalonians. Timothy also received has two letters from Paul in the New Testament but he is a single person not a church.

Source: See Answer

Paul wrote this letter to the head of the church at Crete. Who was the letter sent to?

The letter was sent to Titus. It is better known as the book of Titus

Source:

Titus

This letter was both a thank you and an update on a sick member of the church. What is the letter?

This is the letter to the Philippians. Paul thanked them for their gifts and also updated them on the condition of Epaphroditus. He brought the gifts to Paul.

Source:

Phillippians