Real true joy is only found ultimately in the Lord Jesus Christ. The psalmist says in Psalm 32 v 11, "Be glad in the Lord, and rejoice, ye righteous." The righteous we are told by God are only those with faith in Christ Jesus, having Christ's righteousness reckoned to them on faith in Him. Everything about the character of the Lord Jesus is a joy to all who trust in Him for salvation. The believer in Christ has the joy of knowing that Christ has conquered sin and death for them. What a joy to know He has dealt with our sins against God and saved us from eternal damnation. We are yet to experience the most dreadful moment before us which is death. What a joy to know therefore that God in Christ has forgiven all your sins and will accept you.
It is also a blessing in life, a source of great joy to be ruled by Christ as our Lord. The psalmist in Psalm 19 v 8 speaks of, "The statutes of the Lord are right, rejoicing the heart." We find as a believer in Christ that when out of love for Him we keep His laws, it is a delight and great joy for us. There is so much blessing and true satisfaction in obeying our Saviour.
Finally, it will be eternal joy for the believer to be with Christ. To be with Him, see Him as He is and be like Him will be unspeakable joy! The joy of knowing Christ and experiencing salvation in Him is offered freely to every sinner. God makes it very clear that whoever calls on the name of the Lord shall be saved.
"Let me but Thyself possess,
Total sum of happiness;
Perfect peace I then shall prove,
Heaven below and heaven above."