Train them, remembering continually, the promises of Scripture.
This point is meant to guard you against discouragement.
You have an absolute promise on your side, "Train a child in the way he should go, and when he is old he will not turn from it." [Proverbs 22:6] Think what it is to have such a promise like this.
Promises were the only lamp of hope which cheered the hearts of the patriarchs before the Bible was written. Enoch, Noah, Abraham, Isaac, Jacob, and Joseph—all lived on a few promises, and prospered in their souls. Promises are the energizers which in every age have supported and strengthened the believer. He that has a clear text of Scripture on his side need never be depressed. Fathers and mothers, when your hearts are failing, and ready to give up, look at the words of this text, and take comfort.
Think about who it is that promises. It is not the word of a man, who may lie or repent; it is the Word of the King of kings, who never changes. Has He ever said something, and not done it? Or has He ever spoken a promise, that He will not make good? Neither is anything too hard for Him to perform. The things that are impossible with men are possible with God. Oh, my friend, if we do not receive the benefit of the promise we are dwelling upon, then the fault is not in Him, but in ourselves.
Think, too, what the promise contains, before you refuse to take comfort from it. It speaks of a certain time when good training will especially bear fruit—"when he is old." Surely there is comfort in this. You may not see with your own eyes the result of careful training, for you do not know what blessed fruits may spring from it, long after you are dead and gone. It is not God's way to give everything at once. "Later" is the time when He often chooses to work, both in the things of nature and in the things of grace. "Later" is the season when affliction bears the peaceable fruit of righteousness. [Hebrews 12:11] "Later" was the time when the son who refused to work in his father's vineyard repented and went [Matthew 21:29]. And "later" is the time to which parents must look forward to if they do not quickly see success—you must sow in hope and plant in hope.
"Cast your bread upon the waters," says the Spirit, "for after many days you will find it again." [Ecclesiastes 11:1] I do not doubt, that many children, will rise up in the day of judgment, and bless their parents for good training, who never gave any signs of having profited by it during their parents' lives. Go forward then in faith, and be sure that your labor will not totally be wasted. Three times, Elijah stretch himself upon the widow's child before it revived. Use him as an example and persevere.
The book "The Duties of Parents" can be found here: J.C.