Charles H. Spurgeon on Psalms 89:1

I will sing of the mercies of the Lord for ever. A devout resolve, and very commendable when a man is exercised with great trouble on account of an apparent departure of the Lord from his covenant and promise. Whatever we may observe abroad or experience in our own persons, we ought still to praise God for his mercies, since they most certainly remain the same, whether we can perceive them or not. Sense sings but now and then, but faith is an eternal songster. Whether others sing or not, believers must never give over; in them should be constancy of praise, since God's love to them cannot by any possibility have changed, however providence may seem to frown. We are not only to believe the Lord's goodness, but to rejoice in it evermore; it is the source of all our joy, and as it cannot be dried up, so the stream ought never to fail to flow, or cease to flash in sparkling crystal of song. We have not one, but many mercies to rejoice in, and should therefore multiply the expressions of our thankfulness. It is Jehovah who deigns to deal out to us our daily benefits, and he is the all sufficient and immutable God; therefore our rejoicing in him must never suffer diminution. By no means let his exchequer of glory be deprived of the continual revenue which we owe to it. Even time itself must not bound our praises —they must leap into eternity; he blesses us with eternal mercies —let us sing unto him forever.

With my mouth will I make known thy faithfulness to all generations. The utterances of the present will instruct future generations. What Ethan sung is now a text book for Christians, and will be so as long as this dispensation shall last. We ought to have an eye to posterity in all that we write, for we are the schoolmasters of succeeding ages. Ethan first spoke with his mouth that which he recorded with his pen —a worthy example of using both means of communication; the mouth has a warmer manner than the pen, but the pen's speech lives longest, and is heard farther and wider. While reading this Psalm, such in the freshness of the style, that one seems to hear it gushing from the poet's mouth; he makes the letters live and talk, or, rather, sing to us. Note, that in this second sentence he speaks of faithfulness, which is the mercy of God's mercies —the brightest jewel in the crown of goodness. The grace of an unfaithful God would be a poor subject for music, but unchangeable love and immutable promises demand everlasting songs. In times of trouble it is the divine faithfulness which the soul hangs upon; this is the bower anchor of the soul, its hold fast, and its stay. Because God is, and ever will be, faithful, we have a theme for song which will not be out of date for future generations; it will never be worn out, never be disproved, never be unnecessary, never be an idle subject, valueless to mankind. It will also be always desirable to make it known, for men are too apt to forget it, or to doubt it, when hard times press upon them. We cannot too much multiply testimonies to the Lord's faithful mercy —if our own generation should not need them others will: sceptics are so ready to repeat old doubts and invent new ones that believers should be equally prompt to bring forth evidences both old and new. Whoever may neglect this duty, those who are highly favoured, as Ethan was, should not be backward.