Delight thyself also in the Lord.
This scripture is one of the great litmus tests of the Bible. The unregenerate man cannot delight in The Lord. He delights in food, he delights in sex, he delights in his career, his good fortune, his accomplishments; he even delights in his family. Delighting in God, that is totally off his radar. Delight and God are at opposite ends of the spectrum of the natural man.
But take a look at the born again man. His world has been turned 180 degrees around. He has actually discovered another kind of joy, a joy that comes from heaven. He has discovered the supernatural joy that accompanies God and all that He is involved in. Here is how Charles Spurgeon described this verse.
“The teaching of these words must seem very surprising to those who are strangers to vital godliness, but to the sincere believer it is only the inculcation of a recognized truth. The life of the believer is here described as a delight in God, and we are thus certified of the great fact that true religion overflows with happiness and joy. Ungodly persons and mere professors never look upon religion as a joyful thing; to them it is service, duty, or necessity, but never pleasure or delight. If they attend to religion at all, it is either that they may gain thereby, or else because they dare not do otherwise. The thought of delight in religion is so strange to most men, that no two words in their language stand further apart than holiness and delight. But believers who know Christ, understand that delight and faith are so blessedly united, that the gates of hell cannot prevail to separate them. Such joys, such brimful delights, such overflowing blessednesses, do the saints discover in their Lord, that so far from serving him from custom, they would follow him though all the world cast out his name as evil. We fear not God because of any compulsion; our faith is no fetter, our profession is no bondage, we are not dragged to holiness, nor driven to duty. No, our piety is our pleasure, our hope is our happiness, our duty is our delight.”
To me, this is how I really know if someone is born again. Not that they go to church or have “prayed the prayer”. Is there a real enjoyment found in their godly pursuits. When church, reading the Bible, worship, and even sharing their faith is filled with joy; then I know something real is going on.