We are weak because we are children of Adam - everything is relative to the Most High God, creator and sustainer of all things: we are weak. We only live, move and exist because every moment the Lord Jesus Christ is holding all things together by his word of power. We are dust - we are only more than dust at this moment because God has willed it and spoken it at this moment.
Isaiah 40.28-29So we look forward with sure and certain hope to a body sown in weakness, but raised in power (1 Cor 15:43b).
The LORD is the everlasting God, the Creator of the ends of the earth. He does not faint or grow weary; his understanding is unsearchable. He gives power to the faint, and to him who has no might he increases strength.
All flesh is grass, and all its beauty is like the flower of the field.
The grass withers, the flower fades when the breath of the LORD blows on it; surely the people are grass.
The grass withers, the flower fades, but the word of our God will stand forever.
We are weak because we are sinful and affected by the curse on sin and its effects. Our bodies, emotions and thoughts are weak: they do not function as they were designed but are weak in every part. Furthermore our bodies, emotions and thoughts are sinful in every part: more than weak, we are crippled.
As with the Israelites
Ps 78:35-39We are weak because we are in Christ. What, are we not living by the power of God in him (2 Cor 13:4)? Is there not 'power in the blood'? Yes, but as we see it here, God's plan is power through suffering and death, as in Christ. The resurrection is the culmination of the death! We are weak that God's strength might be shown to his glory, as in the cross. It is a descent into weakness that God's glory would be seen in his strength in us, until we are dead and his power resurrects us, as the culmination of the resurrection already begun in Christ. Even our prayer for strength through God's Spirit (Phil 3.14ff) is so that God may be glorified in the church and in Christ Jesus: we are weak in every way so that in every way it is obvious that any strength is God's, to his glory.
They remembered that God was their rock, the Most High God their redeemer. But they flattered him with their mouths; they lied to him with their tongues. Their heart was not steadfast toward him; they were not faithful to his covenant. Yet he, being compassionate, atoned for their iniquity and did not destroy them; he restrained his anger often and did not stir up all his wrath. He remembered that they were but flesh, a wind that passes and comes not again.
1 Corinthians 1:27-31We may expect to be kept weak in service for the sake of God's glory.
But God chose what is foolish in the world to shame the wise; God chose what is weak in the world to shame the strong; God chose what is low and despised in the world, even things that are not, to bring to nothing things that are, so that no human being might boast in the presence of God. He is the source of your life in Christ Jesus, whom God made our wisdom and our righteousness and sanctification and redemption. Therefore, as it is written, "Let the one who boasts, boast in the Lord."
2 Corinthians 12:9-10Will he not answer the prayer of Philippians 3.14-21, for strength through his Spirit? Yes he will, far more abundantly than we ask or think, to his glory. And as he does so, we will 'have strength to comprehend with all the saints what is the breadth and length and height and depth, and to know the love of Christ that surpasses knowledge, that [we] may be filled with all the fullness of God.' So as he strengthens us by his power, we will grasp increasingly how much greater he is (so 'who is man that you are mindful of him?'), how sinful we are and how weak we are as we are called to join in his ministry and so rely even more on his power at work within us, bringing glory to him.
But he said to me, "My grace is sufficient for you, for my power is made perfect in weakness." Therefore I will boast all the more gladly of my weaknesses, so that the power of Christ may rest upon me. For the sake of Christ, then, I am content with weaknesses, insults, hardships, persecutions, and calamities. For when I am weak, then I am strong.
"You are my strength when I am weak,
You are the treasure that I seek;
You are my all in all."
Since then we have a great high priest who has passed through the heavens, Jesus, the Son of God, let us hold fast our confession. For we do not have a high priest who is unable to sympathize with our weaknesses, but one who in every respect has been tempted as we are, yet without sin. Let us then with confidence draw near to the throne of grace, that we may receive mercy and find grace to help in time of need.