There are all sorts of speculative teachings about this these days, but let me tell why I think that Jesus wrote in the sand …
There is a law found in Numbers 5:11-31 called “the law of jealousies.” This is something which makes provision for making an appeal to the Supreme Court of God to determine guilt or innocence in the event that truth cannot be determined by men. In this law, the priest would actually write the judgments of the law upon a scroll and then submit the case to God for judgment.
Now, as this relates to Jesus and the woman accused of adultery, the woman’s accusers were making an appeal to stone the woman based upon the law of Deut. 22:22, but Jesus knew that the witnesses were not credible, so He appealed to the law found in Numbers 5, which was to bring the whole thing to the Supreme Court of God.
Jesus didn’t have a scroll with him at the time, so He wrote the judgments of the law upon the ground. The woman’s accusers did not realize at first what Jesus was doing, because normally, these things would have been written upon a scroll. They were also appealing to the law of Deut. 22:22, because they assumed that the woman was guilty even before the trial.
Jesus, however, judged her by a different law, that found in Numbers 5. This is because Jesus knew that it would be impossible for the woman to receive a fair trial, and this because the Scribes and Pharisees had ulterior motives. These religious men were trying to even entrap Jesus Himself, and they were willing to sacrifice the woman’s very life to accomplish this end (the wickedness of religious spirits, huh?).
In addition to all of this, it was unlawful at the time for anyone to be put to death without the consent of the Roman authorities. Thus, Jesus could not have sentenced this woman to death even if that had been the correct judgment. So He appealed to the only principle of law applicable at the time. He appealed her case to the Supreme Court and judged her according to Numbers 5 rather than according to Deuteronomy 22:22. At first, the Scribes did not understand what He was doing, and so they pressed Him for a judgment.
Jesus silenced them though, and He did this by saying “He who is without sin among you, let him be the first to throw a stone at her.” He then stooped down and wrote in the sand again. In other words, He told them in this sand-writing that He was appealing to the only One who was perfect enough to judge the case. When Jesus had written enough for them to read, I’m sure that they then recognized just what He was doing. Since their entire purpose was to entrap Him, they knew that they had failed.
One by one, they then went away. Perhaps they knew that when a man appeals to the Supreme Court, God always judges the accusers before judging the accused. He takes the entire situation and judges all sides impartially and completely. The Scribes and Pharisees knew that they had been using this woman unjustly in their attempt to entrap Jesus. Thus, the woman also had a legal case against them. Perhaps they knew they had better drop all charges quickly, or else God would judge them first. Whatever their understanding was, it was not long before all those who had brought the woman to Jesus had left the court room. Jesus and His disciples were left alone with the woman. He asked where her accusers were. There were none. This ended the court case, because there were no witnesses against her. Bottom line of this part of the story is — Jesus beat them at their own game.
Now, the application for us today in this is that everyone has the right to go before God’s Court when they believe that justice is not being rightly served. This is simply a matter of entrusting the case to God Himself – the only One who sees and knows ALL.