"The more sure word of prophecy means a man’s knowing that he is sealed up unto eternal life, by revelation and the spirit of prophecy, through the power of the Holy Priesthood. It is impossible for a man to be saved in ignorance." (D&C 131: 5-6)
We must have a sure knowledge that we are sealed up to eternal life in order to be saved. Guessing about our eternal standing cannot ever save us. Simple hope, a firm belief, a strong conviction that our "many wonderful works" (Matt. 7: 21-23) will eventually lead to eternal life just is not enough. We may be very active in the church and strictly religious in our lives, we may know the Book of Mormon is true, we may have the witness of the Holy Spirit that Jesus is the Christ, we may follow religious leaders devoutly, we may have done "many wonderful works" in the name of The Lord, (Matt. 7: 21-23) however, if we are ignorant of our own actual standing with respect to our eternal life, it will be impossible for us to be saved. It requires actual and real "knowledge."
The particular knowledge that is required is not general in its nature. It is specific and can only be received in one way. That is why not everyone that cries Lord! Lord! will enter into the Kingdom of heaven, but he that doeth the will of my Father which is in heaven." (Matt. 7: 21) And, as we understand now, the will of the Father is that you "receive the Son." (JST John 6:44)
Joseph Smith said it this way:
"knowledge is revelation, hear all ye brethren this grand key; knowledge is the power of God unto salvation...There are two keys, one key knowledge. The other make your calling and election sure. For if you do these things you shall never fall for so an entrance shall be administered unto you abundantly into the the everlasting Kingdom of our Lord and Savior Jesus Christ...We have also a more sure word of prophecy whereunto give heed until the day star arise in your hearts...it is one thing to receive knowledge by the voice of God, (this is my beloved Son &c.) & another to know that you yourself will be saved, to have a positive promise of your own salvation is making your calling and election sure. viz the voice of Jesus saying my beloved thou shalt have eternal life. Brethren never cease struggling until you get this evidence." (Words of the Prophet Joseph Smith Ehat and Cook page 204-208)