C. Stephen Evans explains why there is a difference between proving the existence of the Loch Ness Monster and God:
Religious belief is presumed to be not innocent, but guilty until proven otherwise. Unless we can prove God's existence we must refrain from believing.
People who think like this imagine the religious situation to be something like the following: Suppose you are having an argument with someone over how many species of animals there are. Both of you agree that there are many species-cats, dogs, cows, and so on. You, however, believe in one species which your opponent does not believe in, say, the species of monsters residing in the Loch Ness. Your opponent claims that the burden of proof is on you if you want to believe in such monsters. Without strong positive evidence you would do better to refrain from believing in the Loch Ness monster.
Perhaps in this situation the burden of proof would be on you to come up with evidence for your belief. Perhaps if that evidence is less than conclusive, it would be wiser to suspend or withhold judgment. After all, we don't usually believe in monsters if we have no evidence of their reality. But belief in God is not at all comparable to belief in such a monster.
One important difference is that the Loch Ness monster is merely "one more thing." The two people that disagree about the monster agree about all the other animals. God, however, is not merely "one more thing." The person who believes in God and the person who does not believe in God do not merely disagree about God. They disagree about the very character of the universe. The believer is convinced that each and every thing exists because of God and God's creative activity. The unbeliever is convinced that natural objects exist "on their own," without any ultimate reason or purpose for being. In this situation there are no neutral "safe" facts all parties are agreed on, with one party believing some additional "risky facts." Rather, each side puts forward a certain set of facts and denies its opponents' alleged facts. There is risk on both sides.
A second important difference between the case of God and the case of the Loch Ness monster is that religious beliefs imply something fundamental about how life should be lived. Insofar as religious beliefs embody themselves in actions, suspending judgment is not possible. Even if it were possible to suspend judgment intellectually, it would by no means enable a person to avoid risk. It is clear that the faith of the religious believer and the faith of the atheist are equally risky. It is hard to see why any special burden of proof falls on the religious believer.
(pp.21-22, Why Believe? Reason and Mystery as pointers to God)
Evans is a Kierkegaard scholar, and this seems to echo the Dane's own thought:
The idea of proving the existence of God is of all things the most ridiculous. Either he exists, and then one cannot prove it (no more than I can prove that a certain human being exists; the most I can do is to let something testify to it, but then I presuppose existence) - or he does not exist, and then it cannot be proved at all.
Pointing out that 'it is generally a difficult matter to want to demonstrate that something exists', Climacus prefers the opposite approach:
Therefore, whether I am moving in the world of sensate palpability or in the world of thought, I always draw conclusions from existence, not to existence. For example, I do not demonstrate that a stone exists but that something which exists is a stone. The court of law does not demonstrate that a criminal exists but that the accused, who does indeed exist, is a criminal
(pp.55-56, Sylvia Walsh, Kierkegaard: Thinking Christianly in an existential mode)
Therefore, while it may be unjustifiable to ask whether God the Son exists, we can ask whether Jesus is God the Son. We, and the First Century Jews knew who God is through the Old Testament and through nature. Jesus showed that he was God the Creator and the God of Israel by his power and his love. He fitted, at least if you listened. I think this is what Peter Jensen (?) means by Christology from within [the Biblical narrative], rather than above or below.