In the fifth verse of this surah the prayer addresses God and says: ایاک نعبد و ایاک نستعین
The words نعبد and نستعین have been used in plural form. Even when the prayer is doing his prayer alone he uses these words in plural form.
Surah al-Hamd is cited several times during the daily obligatory and recommended prayers. In fact prayer would be invalid if this surah is not cited.
In the fifth verse of this surah the prayer addresses God and says:ایاک نعبد و ایاک نستعین The words نعبد and نستعین have been used in plural form. Even when the prayer is doing his prayer alone he uses these words in plural form.
One may ask why these words have been use in plural form.
One famous exegesis is that a believer should always consider himself a member of the society of believers. He should not be negletful about other muslims. Also it implies that it is recommended to perform the prayer in the congragational form.
Another exegesis which is given forth by Fakhr Razi in his commentary on the holy Quran is that:
According to the Islamic law when someone sells different goods in one bargain among which are sound and defected ones, the buyer has a right to either accept all of them or reject all of them, not to get those which are sound and give back those whick are flawed.
Here also the prayer does not consider his supplication to be completed and without any defect so in a bid to make sure that his worship should be accepted, he combines his worship with the worship of other believers among whom there are pious people whose prayers are accepted. This way God who has advised his servants not to discriminate between goods in one bargain will not do so himself, so he will accept the worship of the believers altogether.