Scripture, not without reason, commands us to use both continually.
1. We have already described the greatness of our want, while experience itself proclaims the straits which press us on every side to be so numerous and so great, that all have sufficient ground to send forth sighs and groans to God without intermission, and suppliantly [earnestly] implore him.
2. For even should they be exempt from adversity, still the holiest ought to be stimulated first by their sins, and, secondly, by the innumerable assaults of temptation, to long for a remedy.
3. The sacrifice of praise and thanksgiving can never be interrupted without guilt, since God never ceases to load us with favour upon favour, so as to force us to gratitude, however slow and sluggish we may be.
4. In short, so great and widely diffused are the riches of his liberality towards us, so marvellous and wondrous the miracles which we behold on every side, that we never can want a subject and materials for praise and thanksgiving.
To make this somewhat clearer: since all our hopes and resources are placed in God (this has already been fully proved), so that neither our persons nor our interests can prosper without his blessing, we must constantly submit ourselves and our all to him. Then whatever we deliberate, speak, or do, should be deliberated, spoken, and done under his hand and will; in fine, under the hope of his assistance.
God has pronounced a curse upon all who, confiding in themselves or others, form plans and resolutions, who, without regarding his will, or invoking his aid, either plan or attempt to execute (James 4:14; Isaiah 30:1; Isaiah 31:1). And since, as has already been observed, he receives the honour which is due when he is acknowledged to be the author of all good, it follows that, in deriving all good from his hand, we ought continually to express our thankfulness, and that we have no right to use the benefits which proceed from his liberality, if we do not assiduously [diligently] proclaim his praise, and give him thanks, these being the ends for which they are given.
… Hence David, on experiencing the loving-kindness of the Lord, elegantly declares, "He hath put a new song in my mouth" (Ps. 40:3); intimating, that our silence is malignant when we leave his blessings unpraised, seeing every blessing he bestows is a new ground of thanksgiving.
(Taken from John Calvin's Of Prayer—A Perpetual Exercise of Faith.The Daily Benefits Derived from It, pg. 35-36. Formatted for readability.)