Teach me good judgment - The word here rendered “judgment” means, properly, “taste,” that power by which we determine the quality of things as sweet, bitter, sour, etc. Then it is applied to the mind or understanding, as that by which we determine the moral quality of things, or decide what is right or wrong; wise or foolish; good or evil. Here it means that he desired to have in full exercise the faculty of appreciating what is right, and of distinguishing it from what is wrong.
And knowledge - Knowledge of the truth; knowledge of thy will; knowledge of duty.
For I have believed thy commandments - I have confided in thy commandments. He believed that such a keeping of the law of God would be connected with a correct view of things. The keeping of the commands of God is one of the best means of growing in true knowledge, and of cultivating the understanding; of promoting a just taste or perception of what is true, and of developing the powers of the soul in the best proportions. Compare John 7:17.