Here is a great quote from John Calvin that fits well with Psalm 70.
In Book III of The Institutes of the Christian Religion, John Calvin writes:
The very best Christians, when all is calm, fondly think of themselves as steadfast and solid. But once trouble overtakes them, they discover it was all a sham. That, then, is how believers are alerted to their frailties, so that they might be helped to grow in humility, to abandon all sinful confidence in the flesh, and to submit wholly to God’s grace. With submission comes the discovery that God’s power is now available to them: there they have a fortress sufficient for their needs.
Paul makes much the same point, when he writes that from tribulation comes patience, and from patience, test of character (Rom. 5:3-4). Believers experience the truth of the Lord’s promise of help in time of trial, when they endure patiently, upheld by his hand—something they could never do in their own strength. Patience thus provides the saints with proof that God supplies his promised help whenever it is needed. By this means, too, they are encouraged to hope, because it would be gross ingratitude to doubt God’s faithfulness in the future, when in the past they have found him firm and immoveable.
Already we see how many benefits flow to us, as in an unbroken stream, from the cross. By overturning the false ideas we naturally have about our own powers, and by unmasking the hypocrisy which charms and flatters us with its deceits, the cross beats down the arrogance of our flesh which does us untold harm. And once it has humbled us, it teaches us to rest in God who, since he is our foundation, does not let us go under or lose heart. Victory in turn gives rise to hope, in as much as the Lord by fulfilling his promises establishes his faithfulness for all future time.
These considerations alone suffice to show how important it is that the cross should train us. For it is no small gain to be free of the self-love which blinds us, so as to be able rightly to appreciate our weaknesses, to keenly feel them, so as to learn how to distrust ourselves; to distrust ourselves, so as to transfer our trust to God; to lean on God with heartfelt trust, so as to continue, with his help, victorious to the end; to stand firm in his grace, so as to find him true and faithful to his promises; to know the certainty of his promises, so as to strengthen the hope within us.