I Samuel 17:18 And carry these ten cheeses unto the captain of their thousand, and look how thy brethren fare, and take their pledge.
David was sent to see how they were faring and to take their pledge. The commentators are not certain what the pledge refers to. One opinion is that it refers to bringing back proof that his brothers were alive and ok. The idea seems more logical to me and that is that David was carrying their pledge or whatever was needed for any debts that they had incurred as soldiers.
Either way this pledge that David was sent to take gives a good idea of the relationship of the responsibility of the spiritual father to the soldier who is on the field and in the battle. The father on the one hand may have been concerned for their welfare and sent to find out how they were. Pastor you serve as a spiritual father to your missionaries. How often do you concern yourself to send a gift at the hand of a special messenger and send them to find out just how well your missionary is doing? Many times in missions the idea is out of sight out of mind. Not so with a true father and it should never be so with a pastor or spiritual father.
If on the other hand this pledge refers to helping with what ever needs the brothers may have had it is of equal importance. Make sure that he was what he needs. Be sure that you spiritual son is not having to hock what he has to pay the bills. Take his pledge, your faith promise, and meet his needs. It is not enough to boast about having sent out a missionary you must be personally concerned for both their welfare and their financial burdens. After all they are your spiritual sons.