that my joy may be in you, and that your joy may be made full.

John 15:11  These things have I spoken unto you, that my joy may be in you, and that your joy may be made full. 

John 15:11

These things were designed to comfort them by the promise of the Holy Spirit and of eternal life, and to direct them in the discharge of their duty.
My joy - This expression probably denotes the happiness which Jesus had, and would continue to have, by their obedience, love, and fidelity. Their obedience was to Him a source of joy. It was that which He sought and for which He had labored. He now clearly taught them the path of duty, and encouraged them to persevere, notwithstanding He was about to leave them. If they obeyed Him, it would continue to Him to be a source of joy. Christ rejoices in the obedience of all His friends; and, though His happiness is not dependent on them, yet their fidelity is an object which He desires and in which He finds delight. The same sentiment is expressed in John_17:13.
Your joy might be full - That you might be delivered from your despondency and grief at my departure; that you might see the reason why I leave you, be comforted by the Holy Spirit, and be sustained in the arduous trials of your ministry. See 1Jo_1:4; 2Jo_1:12. This promise of the Savior was abundantly fulfilled. The apostles with great frequency speak of the fullness of their joy - joy produced in just the manner promised by the Savior - by the presence of the Holy Spirit. And it showed His great love, that He promised such joy; His infinite knowledge, that, in the midst of their many trials and persecutions, He knew that they would possess it; and the glorious power and loveliness of His gospel, that it could impart such joy amid so many tribulations. See instances of this joy in Act_13:52; Rom_14:17; 2Co_2:3; Gal_5:22; 1Th_1:6; 1Th_2:19-20; 1Th_3:9; 1Pe_1:8; Rom_5:11; 2Co_7:4.