Well, it depends what you mean by useless. If you go to a movie theater and pray that the film you are watching ends one way, then your prayer is useless because the movie will end the way it was choreographed whether you pray or not. Nothing you do in that movie theater will change the end of that movie. ......
Well, if the only purpose of prayer was to change God's mind and get stuff, then I would agree with you completely. It continues to baffle me that this is the Apostolic view. We happen to think that prayer is so much more than getting stuff. Since I was just in there on another post, here is what Calvin says:
Section 3 --- But some one will say, Does he not know without a monitor both what our difficulties are, and what is meet for our interest, so that it seems in some measure superfluous to solicit him by our prayers, as if he were winking, or even sleeping, until aroused by the sound of our voice? Those who argue thus attend not to the end for which the Lord taught us to pray. It was not so much for his sake as for ours. ......
It will be sufficient to refer to the example of Elijah, who being assured of the purpose of God had good ground for the promise of rain which he gives to Ahab, and yet prays anxiously upon his knees, and sends his servant seven times to inquire (1 Kings 18:42); not that he discredits the oracle, but because he knows it to be his duty to lay his desires before God, lest his faith should become drowsy or torpid. Wherefore, although it is true that while we are listless or insensible to our wretchedness, he wakes and watches for use and sometimes even assists us unasked; it is very much for our interest to be constantly supplicating him;
[continuing:] first, that our heart may always be inflamed with a serious and ardent desire of seeking, loving and serving him, while we accustom ourselves to have recourse to him as a sacred anchor in every necessity; secondly, that no desires, no longing whatever, of which we are ashamed to make him the witness, may enter our minds, while we learn to place all our wishes in his sight, and thus pour out our heart before him; and, lastly, that we may be prepared to receive all his benefits with true gratitude and thanksgiving, while our prayers remind us that they proceed from his hand. Moreover, having obtained what we asked, being persuaded that he has answered our prayers, we are led to long more earnestly for his favour, and at the same time have greater pleasure in welcoming the blessings which we perceive to have been obtained by our prayers.
...... It is very absurd, therefore, to dissuade men from prayer, by pretending that Divine Providence, which is always watching over the government of the universes is in vain importuned by our supplications, when, on the contrary, the Lord himself declares, that he is "nigh unto all that call upon him, to all that call upon him in truth (Ps 145:18). No better is the frivolous allegation of others, that it is superfluous to pray for things which the Lord is ready of his own accord to bestow; since it is his pleasure that those very things which flow from his spontaneous liberality should be acknowledged as conceded to our prayers. This is testified by that memorable sentence in the psalms to which many others corresponds: "The eyes of the Lord are upon the righteous, and his ears are open unto their cry" (Ps 34:15). ...... (from Calvin: Of Prayer.) (emphasis added)
Prayer is obviously not useless in ANY sense to us.
In addition to that, in the Reformed theology, even God is boxed in with His plan (the "movie"), which is now done, is perfect and nothing can change it. Not even God.
Yep, I'd hate to be boxed into definitional perfection just like ol' God is. That would be a real mess. Of course you are right that God should be able to correct His own errors. After all, He's only ...... :)
That's the meaning of prayer in the languages of the Bible: asking for mercy, a divine favor. Again, you are confusing prayer with worship (giving praise, adoration), although adoration usually preceeds prayer.
It continues to baffle me that this is the Apostolic view
The Apostolic view what Christ taught. He gave us the Lord's Prayer which starts giving God praise and then asking for Him for essential mercies: bread, forgiveness, protection from the evil one.
Prayer is an appeal to God.
If God is the "chief decider" of what we do then our prayers are not our prayers but mechanical repetitions ordianed by God, and we are mindless robots powered by God. Reformed theology 101.