Paul was trusting in the righteousness of Christ, not in his own righteousness.

Joy is not in where we've been,
Joy is who's waiting, at the end.

Take joy in: 
-The Lord
-Heaven and eternal life 
-Our forgiveness
-Our victories (remember them, talk about them)
-Each other's victories (remember them, talk about them)

Now to Him who is able to keep you from stumbling, And to present you faultless Before the presence of His glory with exceeding joy,

1 Therefore we also, since we are surrounded by so great a cloud of witnesses, let us lay aside every weight, and the sin which so easily ensnares us, and let us run with endurance the race that is set before us, 2 looking unto Jesus, the author and finisher of our faith, who for the joy that was set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God.

4 And God will wipe away every tear from their eyes; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away." 5 Then He who sat on the throne said, "Behold, I make all things new." And He said to me, "Write, for these words are true and faithful." 6 And He said to me, "It is done! I am the Alpha and the Omega, the Beginning and the End. I will give of the fountain of the water of life freely to him who thirsts.

37 Yet in all these things we are more than conquerors through Him who loved us. 38 For I am persuaded that neither death nor life, nor angels nor principalities nor powers, nor things present nor things to come, 39 nor height nor depth, nor any other created thing, shall be able to separate us from the love of God which is in Christ Jesus our Lord.

22 But the fruit of the Spirit is love, joy, peace, longsuffering, kindness, goodness, faithfulness, 23 gentleness, self-control. Against such there is no law.