Today you have one very good reason to be in a good mood! (Please, don't roll your eyes. You do!)
You have a grand reason to be in a good mood . . . despite hardships, hassles, headaches, and heartbreaks . . . despite poor health, poor finances, poor grades, or a poor performance . . . despite bad news, bad breaks, or even a bad, bad backache.
I am not being trite! This is not rah-rah pop psychology. This is tried and true, deep-seated theology. Read closely:
What then shall we say to these things? If God is for us, who can be against us? He who did not spare his own Son but gave him up for us all, how will he not also with him graciously give us all things? Romans 8:31-32 ESV
The gospel is the good news that God did something for you that you could not do for yourself. Jesus sacrificed his life for you on the cross. He took the punishment for your sin, dying, and rising again to give you life. Once and for all God demonstrated that he was for you. He could not have said it any stronger.
Paul's argument in light of this truth is simple. "If God loved you so much to give up his Son on your behalf, don't you think he will give you everything you need?"
Of course he will! Today may be cloudy, but your mood does not have to be.
That is the life-permeating, world-altering, universe-changing truth of the gospel.
The gospel does not erase all your problems, but resting in the truth that God is for you definitely improves the mood. So how does one "rest" in that truth?
Preach it to yourself. Tell yourself, "God is for me!"
Saturate your mind with that truth. Memorize Romans 8:31-32. Listen to songs that remind you of the reality of God's care.
Remind others of God's promise. Reminding them will encourage their hearts while strengthening yours at the same time.
Remember that truth trumps feelings. Resting in your feelings is a ticket to an emotional roller coaster ride with very high highs and very low lows. Truth is truth whether you "feel it" or not.
Offer God prayers of thanksgiving and praise. Redirect your heart to the One who saves it and protects it.
God is for you!
 C. J. Mahaney, The Cross-Centered Life, page 67.