In some homes in America it is polite for a dinner guest to offer to help clean up after the meal. If your friend is moving and needs help loading the moving van, I good friend will lend a hand. There is an American saying, "Many hands make light work." Or "If we all pitch in we can get the work done more quickly." In each of these cases, we could do the work ourselves with no help, but the task would feel daunting.
But spiritual work can only be done by the Holy Spirit. That is why we need to pray for one another that our work in God's kingdom will be blessed by God. If it is not, we work in vain (2 Thessalonians 3:1; Psalm 127:1).
