People do not gain wisdom by any efforts of their own, but God gives it according to the laws of His own goodness.

For the Lord giveth wisdom,.... Natural wisdom in all its branches, with all its improvements, and in its utmost latitude and perfection; and spiritual wisdom, which lies in the knowledge of a man's self, his own folly, impurity, impotence, and misery; being wise unto salvation; in the knowledge of Christ, as the only way of salvation, and of God in Christ; in partaking of the true grace, which is wisdom in the hidden part; in being acquainted experimentally with the doctrines of the Gospel; and in walking wisely and circumspectly, and as becomes it, which is practical wisdom: and all this is the gift of God; as is also Christ, who is wisdom, and is given to be wisdom to his people. He is the gift of God to them, in all characters he bears, and relations he stands in; he is a very large comprehensive gift, an unspeakable one; which is given freely and liberally, and is never taken away again. Now this is said, partly to caution such who search after wisdom, and find it, not to attribute it to their diligence and industry, but to the grace of God; and partly as a direction where to go for it; and as an encouragement to hope to have it, since the Lord freely gives it, James 1:5;
out of his mouth cometh knowledge and understanding; by the prophets of the Old Testament who came with a "Thus saith the Lord", and were the mouth of the Lord to the people; from whence flowed the knowledge of divine things; of the will of God; of the Messiah, his person and offices; of his coming, sufferings, death and salvation by him: and by his Son, by whom he has spoke in these last days, and has declared all his mind; and by whom the doctrines of grace and truth, and the knowledge of them, are come fully and clearly, Hebrews 1:1; and by the Scriptures of truth, both of the Old and of the New Testament, which are the word of God; what are breathed by him and come out of his mouth, and are able to make men wise unto salvation: and by the ministers of the Gospel, who speak in the name of the Lord, and the Lord by them; and by means of whom he imparts much spiritual and evangelical knowledge to the sons of men; the mouth of a Gospel minister, who is the month of God to men, "speaketh wisdom, and his tongue talketh of judgment", Psalm 37:30. This clause is added, to encourage to a search after wisdom in the use of means; namely, by attending on the word, and the ministry of it.

For--God is ready (James 1:5; James 4:8).
out of his mouth--by revelation from Him.