R. Yonah: One who goes early to Beis Din and tells to them his claims, he is vindicated in his words. People are wont to tell their merits, but not their liabilities.

Malbim: This teaches that one should not strive to have judgment and judges; the loss exceeds the gain. Compromise is better. In any case, when there is a doubt, they should cast a lottery and do like it falls. If you want to have judgment, for you think that the judge will vindicate you, indeed, the first will be vindicated in his feud - refer to 18:17:2:3.

R. Yonah #1: What does it help him that he told his claims first to Beis Din, and Hit'im his claims (gave to them taste, i.e. made them seem proper) to the judge in the absence of his opponent? When his opponent comes, the judge will investigate and hear his claims a second time. Not only did it not help - he lost, for he brought himself to suspicion. Perhaps they will suspect that because he claims Sheker, he chose to claim in front of the judge in the absence of his opponent! He could not elaborate to be Mat'im his claims in front of his opponent, who knows that it is Sheker. Chazal forbade to be Mat'im claims in front of the judge in the absence of his opponent (Sanhedrin 7b).

R. Yonah #2: Perhaps "va'Chakaro" commands the judge to investigate him well when he comes, and not to rely on his first words. He should not raise his words into his heart until he hears the other party, and discerns the Emes. Chazal forbade a judge to hear a litigant's claims in the absence of his opponent (Sanhedrin 7b).

Malbim: [Even if the first is vindicated], the other will come and investigate him. You do not know what he will claim against you and contradict your claims!