Towards himself a Christian should have a broken spirit, but towards God it should be one of rejoicing always in Him. He rejoices not for its own sake nor because of any joyful experience, work, blessing or circumstance, but exclusively because God is his center.
Watchman NeeNatural strength is what we receive from the hand of God as Creator. Spiritual strength is what we receive from God in grace.
Watchman NeeOften the children of God cannot rise up to answer the Lord's call to service simply because, though their physical condition is good, their feelings are low, cold, and reluctant. Or even when their emotions are quite high, passionate, and willing, they find themselves unable to serve the Lord because now the body reacts lazily. The disciples found themselves in precisely that situation in the Garden of Gethsemane: "the spirit indeed is willing, but the flesh is weak"
Watchman Nee