It is the nature of Christian faith to be certain, lack of certainty is not Christian faith.
"Faith is being sure of what we hope for and certain of what we do not see." (Hebrews 11:1)
"We know that. . .we know what. . .we know that. . ."(1 John 3:14, 16, 19)
Hebrews 11:1 doesn't speak of epistemological certainty. The author of Hebrews writes that faith is the substance (
hypostasis) of our hope--of all that we have hope in--and the evidence or conviction (
elegchos) of what is unseen.
It is through faith that we are brought into confidence of Gods promises, even though they remain unseen. That we walk by faith rather than sight; trusting in God's promises even when our senses and sense of reason are at odds with them. That we, as Paul says, "see through the glass dimly, but then face to face, knowing even as I am known".
If by "certainty" you mean the strength of confidence, no problem. But that's not what Subdivision means by "certainty"; the discussion of "certainty" is about epistemological certainty.
Epistemologically no, I am not "certain" of the truth of what I believe. I could be wrong. But nevertheless I have confidence in Jesus Christ, confidence in God's promises. I have a confidence in the Gospel that goes beyond reason and and espistemological arguments; a confidence from faith. A faith that I did not give myself, but a faith that comes from outside of myself from God, who gives me faith through the very Gospel in which I now hope, trust, believe, and commit my whole self to in faith.
If epistemological certainty were a requirement, and the one who does not have it does not have Christian faith, this reckons the man's prayer to Jesus in the Gospels, "Lord, I believe! Help my unbelief!" as nonsense.
"Lord I believe, help my unbelief" is the prayer only the Faithful can make.
Doubts, struggles, temptations, all the many nuances and stresses and existential crises of human existence in this world are part of our carrying our cross of discipleship in faith.
Of course we continue with unbelief(s). We are sinful human beings for whom faith is seemingly "unnatural", at least according to the natural wisdom of man. That's why the Apostle says that the things of God are foolishness to the wisdom of the wise, and that the things of God can only be apprehended to us by the Spirit; saying they are "Spiritually discerned". The Apostle speaks of faith by the power of the Spirit.
This is why we are dependent upon Word and Sacrament. Through Word and Sacrament the Spirit is always at work, creating in us faith; faith in the faithful promises of God in Jesus Christ. Though we do not see, though we do not know; we believe, we hope, we trust, we are confident in the God who shows Himself to us in Jesus Christ. So that we know the Father through knowing His Son. And we know God's Son through the Spirit and by the Spirit in Word and Sacrament.
So, again, I hope you're not trying to say that being a Christian means having some kind of absolute epistemological certainty; because to teach and suggest this is to preach and teach against faith. It is from teaching like this that thorns and thistles grow which the Lord warns can choke out faith.
-CryptoLutheran