Charles H. Spurgeon on Psalms 119:68

Thou art good, and doest good. Even in affliction God is good, and does good. This is the confession of experience. God is essential goodness in himself, and in every attribute of his nature he is good in the fullest sense of the term; indeed, he has a monopoly of goodness, for there is none good but one, that is God. His acts are according to his nature: from a pure source flow pure streams. God is not latent and ill active goodness; he displays himself by his doings, he is actively beneficent, he does good. How much good he does no tongue can tell! How good he is no heart can conceive! It is well to worship the Lord as the poet here does by describing him. Facts about God are the best praise of God. All the glory we can give to God is to reflect his own glory upon himself. We can say no more good of God than God is and does. We believe in his goodness, and so honour him by our faith; we admire that goodness, and so glorify him by our love; we declare that goodness, and so magnify him by our testimony.

Teach me thy statutes. The same prayer as before, backed with the same argument. He prays, "Lord be good, and do good to me that I may both be good and do good through thy teaching." The man of God was a learner, and delighted to learn: he ascribed this to the goodness of the Lord, and hoped that for the same reason he would be allowed to remain in the school and learn on till he could perfectly practise every lesson. His chosen class book was the royal statutes, he wanted no other. He knew the sad result of breaking those statutes, and by a painful experience he had been led back to the way of righteousness; and therefore he begged as the greatest possible instance of the divine goodness that he might be taught a perfect knowledge of the law, and a complete conformity to it. He who mourns that he has not kept the word longs to be taught it, and he who rejoices that by grace he has been taught to keep it is not less anxious for the like instruction to be continued to him.

In verse 12, which is the fourth verse of Beth, we have much the same sense as in this fourth verse of Teth.