This question (and the OPs comments) sound like a cry from the heart, addressed to Christians, to see if they know of any literature that would help get them off the agnostic fence. It's probably safe to assume that the fence-sitting agnostic sooner or later becomes really uncomfortable perched on such a hard, narrow bar, and wishes to come down, but on which side?
A major problem for Christians wanting to help is that the agnostic cannot see the matter of God's existence from the Christian point of view. One view is looking into light; the other into darkness. Trouble is, the atheist/agnostic thinks believers in God are staring into impenetrable darkness. So, for them to ask Christians for a torch that may get them 'seeing' God in the darkness, is absurd, for the Christians can only say, "Turn around. You're looking in the wrong direction. Look in the opposite direction where God's light is everywhere."
Therefore, I'm now going to quote extracts from a book entitled, "Behold Your God", written by a Christian, its opening chapter being "Is There Such A Thing As An Atheist?" (For 'atheist', you can equally read 'agnostic'.) The author starts by saying Christians stand between the world and the Word (later explaining how there is the written word of God and the person of Jesus Christ, known as the Word of God, who we read of in the written word - the Bible.)
"The world, unlike the Word, is constantly changing, not least in the
way it understands itself. Today, for example, we describe ourselves
as a secular society. Our laws, our manners, our education and our
culture are entirely divorced from religion. Our society is made up of
atheists. At least, so everyone keeps telling us.
For the Christian communicator this creates enormous problems... Where
can we find a point of contact with a man who believes nothing and to
whom religious language and concepts make no sense (assuming there is
such a man)?... But is it true? Is modern man an atheist?
When we turn to the Bible for answers to such questions we find, first
of all, that it never, anywhere, tries to prove the existence of God.
From Genesis to Revelation it simply assumes that God exists: and that
man knows that He exists.
We find, secondly, that when Paul preaches to the philosophers of
Athens he takes it for granted that they believe in God. He certainly
does not approach them as if they were atheists...
Thirdly, we find Paul in Romans 1:18-32 telling us in so many words
that God has revealed Himself to every human being: 'That which may be
known of God is manifest in them; for God has shown it to them.'
'Since the creation, the invisible things of God are clearly seen,
being understood through the things that are made, so that men are
without excuse.'
This is a theme that goes back to the Old Testament, especially to
Psalm 19: 'The heavens declare the glory of God and the skies proclaim
the work of his hands.'... This has surely lost none of its force with
the passing of the years. A generation which can peer into the
structure of the atom and stand on the surface of the moon has more
reason than even Paul to cry out, 'Oh! the depth of the wisdom and of
the knowledge of God!'
But the revelation is not confined to man's static environment. It
takes place, too, through the movements of history. This was
particularly true of the history of Israel. Time and again God invaded
the lives of his people... But the Gentiles too, experienced God's
revelation through providence. Even when He allowed all the nations to
walk in their own ways, 'He did not leave himself without witness: for
he did good and gave you from heaven rains and fruitful seasons,
satisfying your hearts with food and gladness' (Acts 14:17 & Matthew
5:44 f.). God shows His love or His enemies by making His sun rise on
the evil and on the good and sending rain on the just and on the
unjust.
Even in Romans 1:18-32 Paul is largely concerned with God's revelation
through history rather than His revelation through creation. This is
particularly true o the divine wrath, which is revealed not through
the things that are made but in the life-style to which God has
abandoned civilisation. The degeneracy, vice and idolatry which
prevailed in the Roman empire were themselves demonstrations of the
judicial alertness of God...
[Notice] the phrase 'what may be known' of God. This strongly suggests
that there is a range of truth that may not be known... because only
a little is within man's grasp... He remains a mystery. As Deuteronomy
29:29 reminds us, there will always be 'secret things'. 'Man,' said
Blaise Pascale, 'must not see nothing at all, nor must he see enough
to think that he possesses God, but he must see enough to know that he
has lost him'." Behold Your God pp.22-24, Donald Macleod, Christian
Focus, 1990
There is much more in that chapter, but that point is the right one at which to stop - that we must see enough to know that we have lost God. Any agnostic having a sense of lostness, of needing redirection in life in order to 'discover' God, needs to adjust to that frightening truth. We have lost God. Therefore, we are lost. But God is not lost to those sincerely seeking after him. Turning around to look for God's light (which is all over the place, for those with eyes to see) is the first step in the right direction. God's light has been revealed. No more so than in the person of Jesus Christ, who said himself that no-one comes to God as Father, except through himself, the Son of God.
The book I quoted from is not, however, one I recommend for you to get, for after the next chapter (What Is God?), it majors on the attributes of God. Until the first vital step, of turning around to search in the opposite direction, no progress can be made. Only the sincerely searching agnostic can do that, with God's help.
