In this passage Jesus links truth, keeping his commandments and the Holy Spirit together. I think its a difficult passage to understand. Greek's were obsessed with the search for truth and more recently evangelicals have become obsessed with truth and therefore epistimology. Johns gospel is written probably in about 90AD and in the context of Greek and Roman philosophy and preoccupation of truth so John includes this important discussion to answer questions of his day.
I remember looking for truth and meaning in my life at 14 years old which is why I took myself off to the Congregational Church of my infancy (Streatham) and started to individuate between what I was seeking for and my parents who had taken on a post Christian capitalist ethic devoid of spiritual roots.
By the time I was 17 I had started confirmation classes at the local Anglican church (St Stephens Norbury) and met Dame Cicely Saunders who started the hospice movement in this country and for me epitomised the truth and life I was seeking. For some reason we lose this passion for meaning as we get older. My truth involved a dissatisfaction with an understanding of life linked to materialism and the Conservatives and being part of the status quo of suburban Southern Britain.
Some people look for truth in academic research. I think they will be sadly disenchanted! Long ago I realised that even scientific truth is based on a series of hypothesis which can change. The understanding of the atom is a simple, classic example as we move from static models to wave and energy form.
Truth is not found in aesthetics nor ethics nor in religious rites and doctrine.
Pilate said to Jesus "What is truth?" People can be seduced into false truths with devastating consequences. Look at Fascism or Communism. State truth becomes oppressive.
The Jews in John's gospel represent the orthodoxy of truth of the day. Their tradition gives them a divine right, much like Anglicans in the UK or Roman Catholics in Italy. But this is not truth and anybody who says they have and know the truth is to be avoided like the plague!
Most people dont bother with truth, like my parents they just bumble on through life and manage to avoid asking serious questions even in the face of crisis.
Jesus answer is that he himself is the truth, not a religion or a philosophy. A living reality. He embodied the truth. Not Christian doctrine or rites but Jesus himself! Not semantics about who Jesus was or how you recieve the Holy Spirit or become a Christian, but Jesus himself! Religion and strict adherence often supplants the search for truth, undermines it.
(with thanks to Paul Tillich)