Many of you have heard of the argument against God's omnipotence (all powerfulness) that goes something like this; If God can do anything, can he make a rock so big that even he can't lift it? Of course this is an illogical argument (because if He cannot do either one of them He is not omnipotent, but since it is illogical to do both simultaneously, it is irrational), but it tends to trip people up at first glance. This argument strikes at the heart of whether or not God has the power to enact His will.
Something that hits a little closer to home for the Christians is something like the concept that God want's all men to be saved (c.f. 1 Tim 2:4) but the fact is that not all will be saved (c.f. Mat 7:13-ff). So is God some how limited in his ability to accomplish His will?
Well yes and no.
Yes God is limited in His ability to accomplish His will if you are looking at it for face value, for his will for all men to be saved is not strictly speaking, accomplished. But on the other hand, no He is not limited, except for the ways in which He limits Himself in terms of the means to accomplish His will.
For example, does God have the power and ability strictly speaking to force you to do something He wants you to do? Well, yes He would have that ability technically, but He limits Himself from using that ability because of His character, which is love ... the love that allows you to choose for yourself and the love that causes Him to restrict Himself.
We encounter this idea all of the time. For instance, our precious little Johnny is accused one day of some heinous crime ... and we say, "Our little Johnny could never do that!" But what do we mean by that statement? That little Johnny technically lacks the ability to do that, or that it is against his character to do such a thing? I believe we all recognize that we mean the latter in this instance.
And so it is with God. Of course God has the ability to do what ever He wants, for He is not lacking in power (omnipotence), but He chooses to restrict Himself in order to be consistent with His character, how He defines Himself. And in the example used previously, God defines Himself as love, which does not override the gift He has endowed His creation of man that bears His image ... a will of his own. Thankfully the difference between God and our little Johnny is that God has the power (unlike poor Johnny) to actually enact His character consistently and perfectly, never faulting from it (Num 23:19).