Psalm 64:10 The righteous shall be glad in the Lord, and shall trust in him; and all the upright in heart shall glory.
The believer is accounted righteous because of faith in Jesus. Therefore, he responds to this work of Christ by being glad and rejoicing in the Lord. Joy is the fruit of the Spirit, and such gladness characterizes the life of the Christian. And no matter what happens he maintains a joyful spirit, for he trusts in Him for all things.
The Lord grants an upright heart, and because of that imputed righteousness we glory in the Lord. To glory is to boast in the cross of Christ and brag on God about how great and good He is. To glory is to live in God’s reflected glory, which we enjoy by grace through faith. The glory and kindness of God is reflected in us and comes out through us. God is always good, and we glory in that truth.