Translation
The one who believes in the SON OF GOD has the testimony in himself. The one who is not believing THEOS,
Go to footnote numberhas made Him a liar because he has not believed in the testimony that THEOS has testified concerning HIS SON.
Paraphrase
The person whose life is characterized by faith in GOD has accepted the proof and holds it deep within him. However, the one who does not trust the evidence provided by THE CREATOR AND OWNER OF ALL THINGS, must consider Him a liar because he has heard the evidence provided by THE CREATOR AND OWNER OF ALL THINGS indicating that HIS CO-REGENT is Jesus, and he has rejected it.
Footnotes
1
Here the Greek text has a different grammatical form of the name for God but I keep it as Theos because I want the reader to recognize it and not be confused.