"For the kingdom of God is not a matter of eating and drinking but of righteousness and peace and joy in the Holy Spirit. Whoever thus serves Christ is acceptable to God and approved by men." vs17-18
The kingdom of God is not what we think. It is righteousness, peace, and joy. It's serving God by the Spirit's power. It has nothing to do with this world.
A man can be rich or poor… sick or healthy… and be fully involved in this kingdom, and reaping the benefits, because the reward is spiritual, and so are the promises.
God hasn't promised us an easy life. He's promised God in our life - the life of God in the soul. He's promised us obedience, the joy of forgiveness, and the power of his presence. Seek these things, and everything else will be added. Live for God.
First, it's "not in meat and drink." It's not in petty religious rules, and mere externals. It's not in judging each other, looking down on each other, and disregarding each other.
It's not in what day you worship, or what you eat. We answer to the Lord, and love each other. It's not in being better than others. It's being non judgmental, and helping others up. It's realizing our righteousness is Christ, and doing good is his commandment.
Secondly, it's "righteousness, peace, and joy." God gives imputed righteousness, a righteous soul, and he gives us good works. He gives us the joy of the kingdom, and the peace of believing.
His peace is not of this world. John 14:27, "Peace I leave with you; My peace I give to you; not as the world gives do I give to you. Do not let your heart be troubled, nor let it be fearful." Don't fear that it will be lacking. Let no one trouble you with, "God is not enough." Do his will from the heart, and you'll experience his favor. Go all out for the kingdom, and joy will result. Seek it by faith, and not by self righteousness. Serve sincerely, rather than for selfish gain. God will give what he has promised. Ephesians 6:8, "knowing that whatever good thing each one does, this he will receive back from the Lord, whether slave or free."
Thirdly, it's "in the Holy Spirit." It's not in the world, in money, or in circumstances. It's in the spiritual power of God, who dwells within. It's a comfort that's out of this world, because the Creators inside of us.
Many are looking for joy and passion. They try this and that, but it never sinks in that faithful obedience fulfills us. They never think the God of the Bible gives good by the Spirit. They seek it in externals, saying, "Give me this," but they don't cry out for him. Practical atheism believes joy's in things, rather than in our Redeemer. It's the feeling that he won't satisfy, but something else will.
Of course, this is wrong and deceitful. Go to God for pleasure. Pursue him for joy. It's not in the world; it's walking with God, doing his will from the heart, and receiving your treasures, which cannot be seen.
Finally, we must be redirected upward for the happiness that we seek. Rejoice in good circumstances, but seek the kingdom. Everything else will be added, according to God's kindness and wisdom. He's a joy giver!