"But in your hearts set apart Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience, so that those who speak maliciously against your good behavior in Christ may be ashamed of their slander." ~ 1 Peter 3:15-16
"At the moment I'm not exactly in a very good mood. Torn apart trying to decide what to do with my time. There are a few things bothering me; whether my schedule is too much for me to take and whether I should try to cut down the amount of things I'm doing, or whether I should just carry on and surrender my time, my wants and my effort to God... I'm thinking how little time I actually have even on a Sunday..." ~ Fleetpaw

It is my feeling that the marketing principle, "We can't be everything to everyone" is applicable even in the context of serving. Think of it this way, what if we saw a beggar on the road and he asked for some money? If you are as generous as I thought, you might well give him the money he needed. Imagine then you met such beggars twenty times in a row, will you give to all of them then? Next, think of the millions that are starving in poverty, what are you going to do with them?

We might have good intention when we give to the first beggar, some might even give to the twenty if he is economically capable. But it has to stop somewhere. Thus the very first lesson that we learnt from this is that we are limited in resources, and limited beings we are. We may have the heart to help every single one of those people on earth, if possible, but that is practically impossible simply for the reason that we are not the Savior of this world. If we can, God is we. But that's not true.

Well, you may now be thinking about what Paul wrote about being everything to everyone, so that they might be saved, but that is not in contradiction to what is being said here. When Paul decided to preach in Athens, he immediately loses the chance to preach elsewhere. There is something call the opportunity cost concept working here. When we decide to do a certain thing, we incurred the opportunity cost to do other things immediately.

Thus, we will have to come to the conclusion that we can't be available to all vacancies of various ministry postings, despite the needs. We might think that it is more honorable or rewarding to do everything, but that is not true either. After all, we are limited physically and the reality of tiredness and the feeling of burnt out will soon got the better of us. Availability is an important element when it comes to serving.

Therefore, it is perfectly right to "No" sometimes in the context of serving, and we shouldn't even feel guilty about it, if we are sure we are led to do so. Hence, serving is not a matter of what I want to do, but what God wants me to do. Pray and ask God where He intends for us to be, to accomplish the good works that He has prepared in advance for us to do, in Christ Jesus, and grant us the wisdom not to excuse ourselves from serving by rationalizing.