You write: it says in the Gospel that at the end of the world, evil will triumph over good. This is nowhere stated in the Gospel; it only says that “in the last times, faith will decrease (cf. Lk. 18:8), and, Because iniquity shall abound, the love of many shall wax cold (Mt. 24:12). And the holy apostle Paul says that before the Second Coming of the Savior, that man of sin will be revealed, the son of perdition; Who opposeth and exalteth himself above all that is called God (2 Thess. 2:3–4), that is, the antichrist. But then he immediately says, And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming (2 Thess. 2:8). Where do you see the triumph of evil over good here? In fact, any triumph of evil over good is merely illusory and temporary.—St. Ambrose of Optina.
God created man good and pure. After the fall of Adam, sin and evil entered into human nature. In order to deliver man from this evil, according to God’s judgment it was necessary that God—the second Person of the Holy Trinity—become man and redeem man from that evil he bore. Man’s redemption was wrought by our Lord Jesus Christ on Golgotha, on the Cross, through His suffering, death, and Resurrection. We must believe in this. This is the foundation of our faith. Besides this, Christ gave man His commandments, which teach how people should live in order to be His followers and disciples; in order to do His will for the sake of the soul’s eternal salvation. Whoever accepts Christ the Redeemer and the holy Gospel laws with his heart and lives accordingly will become a Christian, but whoever rejects or neglects them will remain with only his fallen nature, in which goodness was initially mixed with evil cannot be called a Christian; he is alien to Christian life and Christ’s salvation. The enemy tries, masked in the goodness that remains in fallen nature, to distract everyone from Christ, cunningly trying to show that fallen goodness is the only goodness—for thus it seems to someone who does not know Christ’s teachings. Whoever holds fast to the Gospel teachings, despite all the enemy’s seductions, will inevitably experience an inner struggle. Fallen nature loves itself and loves this world, while the Gospel demands self-sacrifice and love for God. Therefore there can never be any concord between them.—St. Nikon of Optina.