"We believe in the same organization that existed in the primitive church, namely apostles, prophets, pastors, teachers, evangelists and so forth." (Articles of Faith 1:6)
Faithful Latter-day Saints sustain members of the First Presidency and the Quorum of the Twelve Apostles as prophets, seers and revelators. As such, we strive to follow these men when they lead us in their ecclesiastical capacity, believing that they speak for the Lord in guiding His church.
That said, we know they are not infallible, and we know from history that sometimes they are wrong, or their decisions are reversed by later church administrations.
One wonders then, what am I to do when I hear a prophet speak? How do I know he speaks for the Lord? How do I reconcile what someone else said that was apparently not speaking for the Lord (because it has been shown to be incorrect or it has been changed by later prophets)?
I respect that this question is not an easy one for many people. It may cause some to look at each pronouncement from the brethren wondering if it is also wrong or temporary. Others take a different approach, choosing to focus on the words of today's prophets without considering historical issues, thereby avoiding the conflict.
For years mine was the latter approach, largely out of my own lack of awareness of church history. More recently I've read more (and there's been more to read). But I still am comfortable taking the approach of trusting today's prophets when they speak.
I can do this for several reasons.
First, my testimony has come in stages in my life. I suppose my first testimony was of the Savior, that He lives and loves me. And that probably pre-dates my joining the church with my family when I was a child, and has grown over time. My second testimony was a general sense that the church is true, and it came quite early in my life (around age 10), largely because of feelings I had when I was baptized and then later when I was sealed to my parents.
Later I gained a specific testimony of the Book of Mormon, and of the restoration of the church. My testimony of Joseph Smith as a prophet has come also in bits and pieces along the way. The truth of the Book of Mormon contributed to it. The peace that I feel in the temple contributes to it. My own experiences with priesthood blessings contribute to it. And my study over the years has contributed, as well.
As for the present prophets (the First Presidency and Quorum of the Twelve), my testimony is strengthened as I raise my hand to sustain them, as I hear their words in conferences and read them, as well, and mostly as I follow their counsel. It comes as the Spirit bears witness to me in quiet moments of prayer and contemplation.
Second, when I have followed their counsel in the past, I have felt the Lord's blessing in my life. There are specific decisions I've made based on specific counsel from the prophets over time. Those choices have not led me astray and in fact have worked to my benefit.
That I sustain them does not mean that I understand or even accept every word each of them says. There are some issues that I still sort through over time. But still I can accept them as inspired men, called of God to do the work they do. And I am confident that as I follow their counsel I will be blessed. And if there are some questions I have about what one or another of them teaches, I can put that on the shelf for the time being. My experience has taught me that those things resolve themselves in time.
I am grateful we live in a time of prophets.