Albert Barnes Commentary 1 Kings 3:12

"behold, I have done according to thy word: lo, I have given thee a wise and an understanding heart; so that there hath been none like thee before thee, neither after thee shall any arise like unto thee." — 1 Kings 3:12 (ASV)

A wise and an understanding heart - Solomon’s wisdom seems to have been both moral and intellectual (see 1 Kings 4:29–34). However, it was moral wisdom alone that he requested and that was promised to him. The terms translated “wise” and “understanding” both denote practical wisdom (see Genesis 41:33, 39; Deuteronomy 4:6; Proverbs 1:2, etc.).

Neither after thee shall any arise like unto thee - That is, in the knowledge of what was in man and in the wisdom to direct the paths of men, he was to be the wisest of “all” mere men. In such wisdom, the world would know only one greater than Solomon (Matthew 12:42; Luke 11:31).