A fourth reason, and perhaps the most subtle, is his failure to live and share what he had learned concerning God's Word. Mark had this to say about one failing to continue to grow, or worse, regressing in his knowledge of the things of the Lord:
"And He said unto them, Is a candle brought to be put under a bushel, or under a bed? and not to be set on a candlestick? For there is nothing hid, which shall not be manifested; neither was any thing kept secret, but that it should come abroad. If any man have ears to hear, let him hear. And he said unto them, Take heed what ye hear: with what measure ye mete (share with others), it shall be measured to you: and unto you that hear shall more be given. For he that hath, to him shall be given: and he that hath not, from him shall be taken even that which he hath" (Mk. 4:21-25).
Alzheimer's is quite similar. Patients begin having trouble remembering short-term memories, but remember things from early in their lives. It is believed this ability to remember long-term memories is due to the patient having shared specific life experiences with others over the years. In other words, those memories are more often rehearsed. Gradually, however, even long-term memories "disappear."
Our love for God should motivate us to obey His Word. Our love for the souls of others ought to cause us to share our greatest possession: our faith in Jesus Christ!
If you don't share what you know, you will forget what He taught you!