This is a covenant. This is the Lord promising. His word cannot fail. He is establishing for you the means by which you can have as your guide and companion His Spirit. His light. His presence in your life.
There is more going on here than an ordinance and a testimony. This is the means by which a link is formed that can and will result in the Father taking that which is corruptible and changing it into that which is incorruptible. Though, like Christ, a man or woman may be required to lay down their life, they shall have power given them to take it up again. For that which has been touched by the incorruptible power of His Spirit cannot be left without hope in the grave. All such people die firm in the knowledge they are promised a glorious resurrection. (D&C 138: 14.)
This, then, is eternal life.