That Good Thing

2 Timothy 1:14 KJV
That good thing which was committed unto thee keep by the Holy Ghost which dwelleth in us.

In the context of the passage, I expect that the "good thing" the passage refers to is the "form of sound words" or the doctrine that had been committed to Timothy through the years of being trained under Paul. Paul speaks of the gift of God which was in Timothy by the putting on of his hands (vs 6).

I think that the vagueness of the term "good thing" allows us to apply it in a number of ways
The good thing of salvation
The good thing of God's Word
The good thing of the church to which we belong
The good thing of the ministry we might have in our church

Whatever good thing God has committed to us must be kept by the Holy Ghost.
It must not be neglected
It will not do its work if it is taken for granted
It cannot grow without nurture
God has given us His Holy Ghost. His work in our lives is to help us grow and increase more and more in the things of God.

May we keep that good thing God has given us growing and increasing and abounding by the Holy Ghost which dwells in us.