Walking in The Light of Testimony by Harold B. Lee
" The time is coming and facing you right now...when except you have that testimony of certainty that these things [the gospel, the Church, and so on] are true you will not be able to weather the storms that are going to beat upon you and try to tear you from your moorings today.
But if you know with all your soul that these things are true... you will know who Jesus your Savior is and who God your Father is; you will know what the influence of the Holy Ghost is. If you know those things you will stand as an anchor against all the storms that shall beat upon your house, as the Master's parable described. That one who hears His words and keeps His commandments shall be as the house that was build upon a rock, and when the storms came and the floods beat upon the house and the winds blew, it fell not, because it was founded upon a rock.
"And every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand: And the rain descended, and the floods came, and the winds blew, and beat upon that house,; and it fell: and great was the fall of it: (Matthew 7:26-27)."
Teachings of Presidents of the Church – Harold B. Lee, p 44