How can fear of worldly concerns be reconciled with trust and reliance upon God?

Taking the means of livelihood and arranging future matters does not contradict reliance on God. The heart relies on God while the limbs work, knowing that the entire matter is in God's hands. The Prophet, peace and blessings be upon him, saved a year's worth of provisions for his family, and this is not considered having prolonged hopes but rather preparation for need, just as Shu'ayb hired Moses, peace be upon them both.