Trinitarian Christians claim to be monotheists thought their subgod Jesus has lesser qualities in common than many polytheists their main god and subgods. God may perhaps not to be found in perceivable attributes but when looking around and reading the Bible like the words are written in that book then it should not be so difficult and not so confusing to come and see Who God really is.
Though many things may be very difficult to proof that does not mean that they would not exist. Also feelings and experiences are difficult to proof, though the results of a God-Being in our life is something what many feel. One thing is for sure: "If God does not exist, then everything is permitted". In the transcendent reality we can not see nor fully understand God but somehow looking around us and listening to our inner feeling each person should be able to come to recognise the Supreme Power and to understand that reality is shaped by a Power beyond us.