For the Lord God is a sun - The Septuagint and the Latin Vulgate render this, “For the Lord loveth mercy and truth.” Our translation, however, is the correct one. The sun gives light, warmth, beauty, to the creation; so God is the source of light, joy, happiness, to the soul. Compare Isaiah 60:19; Revelation 21:23; Revelation 22:5.
And shield - See Psalms 84:9.
The Lord will give grace and glory - Grace, or favor, here; glory, or honor, in the world to come. He will bestow all needful favor on his people in this life; he will admit them to glory in the world to come. Grace and glory are connected. The bestowment of the one will be followed by the other. Romans 8:29-30. He that partakes of the grace of God on earth will partake of glory in heaven. Grace comes before glory; glory always follows where grace is given.
No good thing will he withhold ... - Nothing really good; nothing that man really needs; nothing pertaining to this life, nothing necessary to prepare for the life to come. Compare 1 Timothy 4:8; Philippians 4:19.