Reading the Old Testament Prophets with a heart that believes that our God will keep ALL of His promises can be very encouraging for the child of God. Consider Malachi 3:13-18 next time you are tempted to wonder if you have served the Lord in vain:
“Your words have been arrogant against Me,” says the Lord. “Yet you say, ‘What have we spoken against You?’ You have said, ‘It is vain to serve God; and what profit is it that we have kept His charge, and that we have walked in mourning before the Lord of hosts? So now we call the arrogant blessed; not only are the doers of wickedness built up but they also test God and escape.’”
Then those who feared the Lord spoke to one another, and the Lord gave attention and heard it, and a book of remembrance was written before Him for those who fear the Lord and who esteem His name. “They will be mine,” says the Lord of hosts, “on the day that I prepare My own possession, and I will spare them as a man spares his own son who serves him.” So you will again distinguish between the righteous and the wicked between the one who serves God and the one who does not serve Him.