I'm sure that this has been covered, but this might help someone understand the Significance of this Change.
As many are aware, the Organized Book served as The Instruction manual to Most WTBS topics for a while.
Here is a Link to the PDF of OF Book if you can use it :Organized Book PDF
Who Really is the Faithful & Discreet Slave?
Quote: Why Trust the Faithful & Discreet Slave?
From - Organized to Do Jehovah's Will
So "the faithful steward, the discreet one," must symbolize the composite body of Christ's spirit-anointed footstep followers who live on earth at any given time.
Christ uses this body to publish information on the fulfillment of Bible prophecies and to give timely direction on the application of Bible principles in daily life.
What, then, are the "belongings"? These are all the spiritual assets on earth that have become Christ's property in connection with his authority as heavenly King.Included are facilities at the headquarters of Jehovah's Witnesses, along with branch offices, Kingdom Halls, and Assembly Halls worldwide.
" A great crowd . . . out of all nations and tribes and peoples and tongues," who will survive the great tribulation. - They are among the precious "belongings" of Christ and are greatly loved by the slave class for their loyal, zealous support.
The Governing Body also continues to carry the responsibility of overseeing the preaching work, producing Bible study material, and arranging for the appointment of overseers to serve in various capacities in the organization. These are some of the Kingdom interests of Christ that are being cared for today.
There are many reasons to have complete trust in the slave class.
First and foremost , Jesus has appointed them over all his precious "belongings." This is a clear indication that he has complete trust in them.
God's Word admonishes Christians to cooperate fully with those taking the lead. Why is this to our advantage? As recorded at Hebrews 13:17, the apostle Paul stated: "Be obedient to those who are taking the lead among you and be submissive, for they are keeping watch over your souls as those who will render an account; that they may do this with joy and not with sighing, for this would be damaging to you." For our spiritual protection and well-being, it is incumbent (Necessary as a Duty or Responsibility) upon us to be obedient and submissive to direction from overseers as they 'keep watch over our souls.'
New Understanding Watchtower July 15 2013 - Tell Us, When Will These Things Be?
V-17 We understood that the “arriving” mentioned in verse 46 was linked to the time when Jesus came to inspect the spiritual condition of the anointed in 1918 and that the appointment of the slave over all the Master’s belongings occurred in 1919.
However, a further consideration of Jesus’ prophecy indicates that an adjustment in our understanding of the timing of certain aspects of Jesus’ prophecy is needed. Why so?
V-18 "So it is reasonable to conclude that Jesus arrival to appoint the faithful slave over all his belongings, mentioned at Matthew 24:46, 47, also applies to his future coming, during the great tribulation.Indeed, a consideration of Jesus’ prophecy in its entirety makes it clear that each of these eight references to his coming applies to the future time of judgment during the great tribulation."
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To quickly Summarize : The Primary reason given for us to Trust the Faithful & Discreet Slave,is that Jesus Trusted them and appointed them over all of his Belongings Including the Great Crowd, in 1919.
The NEW Understanding tells us that the Faithful & Discreet Slave IS NOT appointed over all of his Belongings until the Great Tribulation.
According to the Organized Book - "The First and Foremost Reason to Trust " THE FAITHFUL AND DISCREET SLAVE " is Jesus has appointed them over all his precious "belongings." This is a clear indication that he has complete trust in them."