Jesus said to them, “My food is to do the will of Him who sent Me, and to finish His work. (John 4:34 NKJV)
A wonderful feature of spiritual ministry is that it refreshes the one who engages in it. Take, for example, the incident of Jesus at the well of Sychar. He was genuinely thirsty when He asked the woman for a drink, but He ignored His own condition. Instead He engaged her in a conversation that ministered the water of life to her soul.
Then the disciples returned. To their surprise, the Lord looked so refreshed that they began to ask one another where this provision had come from the answer was, of course, that in giving another to drink of the living water, He himself had found His own thirst satisfied. Life in the Spirit and ministry in the Spirit are always like this.