God's Spirit has a COMFORTING virtue. Sadness may arise in a gracious heart (Psalm 43:5). As the heaven, though it is a bright and lucid body, still has interposed clouds, this sadness is caused usually through the malice of Satan, who, if he cannot destroy us, will disturb us. But God's Spirit within us, sweetly cheers and revives. He is called the parakletos, "the Comforter" (John 14:16). These comforts are real and infallible. Hence it is called "the seal of the Spirit" (Eph. 1:13). When a deed is sealed, it is firm and unquestionable. So when a Christian has the seal of the Spirit, his comforts are confirmed. Every godly man has these revivings of the Spirit in some degree; he has the seeds and beginnings of joy, though the flower is not fully ripe and blown. (pg. 71)
παράκλητος, the Comforter, the one who comes alongside to carry our burdens.
And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; (John 14:16 KJV)
I personally don't know how unbelievers trudge through this world without the sustaining assistance of the Holy Spirit. The burdens, challenges, disappointments, hurts, and pains (the interposed clouds) of life are difficult to face even with our Comforter at hand, how dismally depressing it would be to face them without His constant care and presence.