When making a decision, can a judge use the bible or must he go strictly by the statutes?
Yes, a judge may use the bible when making a decision. However, the usage nearly always takes the form of citation (in the form of scholarly texts) rather than precedent.
That said, the lines get blurry sometimes. In Banks v. Maxwell, 171 S.E. 70 (N.C. 1933), the N.C. Supreme Court was tasked with resolving a dispute where the plaintiff had been gored by a bull. As a means of anchoring precedent and establishing a strict liability rule when a bull has previously gored, it stated "[t]he familiar rule of liability for injuries inflicted by cattle has remained approximately constant for more than 3,000 years. This rule of liability was expressed by Moses in the following words..." The court goes on to cite Exodus 21:28-30.
In most secular jurisdictions, the judge must rule solely on the law; statute and (in common-law jurisdictions) precedent. Not even the Vatican uses the bible in judgements.
The bible may be used in court to allow those who choose to do so to take their oath on it. Non-Christians, of course, may use another holy text and it is open to anyone to take an affirmation instead of an oath.
Countries using sharia law will look to the Quran and the Hadiths.