I had my mind blown the other night as I was talking to a friend and wrestling with the question that many Christians ask themselves at some point in their lives: ‘How do I know that I have believed?’
Was it when I was 5 and prayed a prayer to ask Jesus into my heart?
Was it when I was 12 and cried out to God because I was afraid of hell?
Was it when I was 22 and saw deep into my heart and recognised its sinfulness?
See the thing is, I feel that my comprehension of the gospel is so much greater now and it makes me wonder how I ever could have understood enough to have saving faith at age 5. I mean, I’d never even heard words like propitiation or atonement, and I couldn’t fully comprehend death or resurrection or depravity or righteousness. So how did I believe in things I knew nothing of?
The penny dropped last night. My faith is not my own. It is a gift from God. My saving faith at age 5 was not incomplete. It was not reliant on further revelation or deeper knowledge. As God’s gift to me it contained within it the fullness of that which is required for salvation. It was all there. I just didn’t understand it all yet.
If faith and belief were reliant on full comprehension then none of us could ever attain it.
sarsrose 
Thank you for this. You echoed many of the things I wrestle with, and I’m an old man. I’m thankful that the “completeness” of which you speak, though not with that word, is found in the Lord Jesus and in Him I have, and you have, all that we will ever need, Col. 2:10. As far as the “full comprehension” you mentioned, Ephesians 2:7 tells us that it’ll take God Himself “the ages to come” to show us “the exceeding riches of his grace in his kindness toward us in Christ Jesus.” Since that is the case, i don’t think we get much more than the first few lines of the foreword, if you will, of His teaching in this life. Thanks again, and God’s best to you and yours.