"To the faithful you show yourself faithful, to the blameless you show yourself blameless, to the pure you show yourself pure, but to the devious you show yourself shrewd." (Ps 18,25-26) In order to know God, one needs a certain degree of sincerity, of the purity of heart. Without it, he will pass by God internally, he will not believe him - the life has taught him there is nothing higher, nothing pure. (And even if it seems so, in the end it all turns out to be a scam anyway). One translation of the verse 27 even says that God "treats the foul crooked." This does not mean that God necessarily wants to play a false game with someone, nevertheless a crooked person really perceives it that way from his point of view. ("Sorry, but this religion doesn't work.")

God does not let himself known to anyone, because not everyone is willing to it. One must choose a complete sincerity towards God, otherwise God will escape him.