Sometimes as members of the Church of Jesus Christ of Latter-day Saints, we create a false dichotomy between having a testimony and not having one.
In reality, the model provided by Alma 32 and Ether 3 gives a more gradual process of growth in belief and testimony. Alma 32 illustrates the following steps:
1. Desire to believe/willingness to try living the Gospel
2. Knowledge that the Gospel is a good thing/knowledge that it feels right.
3. Enduring to the end on faith which leads to partaking of the love of God freely.
Ether 3 shows the transition from a simple testimony that the Gospel is good to an absolutely certain knowledge of Jesus Christ. While we just know that the Gospel is a good thing, we must live the Gospel on faith that Jesus is who He says He is. Eventually, however, like the brother of Jared, we can know certainly that it is all true.
When we say that we know that Gospel is true, we do, but we still live it on faith, because we do not know God personally, face to face. This is the kind of certain knowledge that is the "great and last promise" of the Doctrine and Covenants. Since knowledge of God is the greatest gift we can receive, we should diligently pray to receive a greater--eventually a certain--knowledge of Him through the Holy Ghost, and, someday, in person.