I explained that a testimony is nothing more or less than the Holy Ghost bearing witness to our soul of the truthfulness of the gospel and of the restored Church.

The Spirit-filled experiences of a mission establish a foundation of faith that can bless you throughout your life. That foundation of faith can be diminished only through neglect or sin.

Recently I interviewed a returned missionary who is less active and claimed to have lost his faith. I asked him if he was praying and studying the Book of Mormon, as he did when he was a missionary. He said he wasn’t because he had lost his faith in Joseph Smith.

I felt prompted to ask him this question: “Are you into pornography?” He answered yes. I told him it was no wonder he had lost his testimony.

I explained that a testimony is nothing more or less than the Holy Ghost bearing witness to our soul of the truthfulness of the gospel and of the restored Church. When we fail to pray and study the scriptures, the influence of the Spirit in our life is weakened, lowering our resistance to temptation. When we sin and become unclean, we lose the companionship of the Holy Ghost altogether. Without the ongoing witness of the Spirit, we can easily begin to think we don’t have a testimony and maybe never did.

Our testimony needs to be continually nourished. That nourishment comes from personal prayer, daily scripture study—particularly the Book of Mormon—and serving in the Church throughout our life.
Prophetic Principles of Faithfulness, C. Scott, Grow, Ensign January 2017