Certainly there was ample opportunity for the Apostles to include such a title in their writings ...
Quite honestly, our knowledge of God develops over time as we pore over His Word (whether oral or written). Did the Patriarchs understand everything God told them? I contend that the Apostles did not KNOW everything about God - and that the Spirit continues to reveal more about Himself through the Apostolic teachings already given.
I wouldn't necessarily disagree (or agree) that our knowledge of God has increased beyond that of the Apostles.
What is a concern is when the church of God requires that these developed beliefs must be accepted by christians ... to be in good standing with the Church.
In other words ... the bar is continually being raised ... and it is much higher now ... than what Christ originally established.John 3:16 For God so loved the world, that He gave His only begotten Son, that whosoever believeth on Him might not perish, but have everlasting life.
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John 6:40 And this is the will of him that sent me, that every one which seeth the Son, and believeth on him, may have everlasting life: and I will raise him up at the last day.
Yes, that is a good point worth discussing. I suppose it comes down to believing that Christ established a community that would continue in His teachings and that all was not made crystal clear to even the first Christians. It appears it is God's way that man explore and build on various knowledge, whether it is regarding science or religion. God condescends to our level, as we see in Scriptures. Thus, He works at our "speed" of "getting it".
Now, with this gradual understanding in mind, we also should keep in mind that the Church was given the power to bind and loosen - and that heaven would witness and vouch for this authoritative teachings and judgments. As such, when the mind of the Church (inspired by the Spirit) leads us to understand a previously shady part of revelation, we gradually come to accept it as God's Word to us. This is not an overnight process.
Regards