On the authority of the son of `Umar ibn al-Khattab radi Allaahu 'anhumaa, who said: I heard the Messenger of Allah (pbuh) say:
Islam has been built on five [pillars]: testifying that there is no deity worthy of worship except Allah and that Muhammad is the Messenger of Allah, establishing the salah (prayer), paying the Zakah (obligatory charity), making the Hajj (pilgrimage) to the House, and fasting in Ramadan. [related by al-Bukhari and Muslim]
And in the Hadith occurs the phrase 'establishment' of the prayer (iqaam as-salah), as opposed to 'performance' of the prayer. The scholars have mentioned how this indicates that the Prayer must be performed in the most perfect manner, after having completed the wudu' in the most perfect manner, and in the Masjid with the jamaa'ah for the men, and so on and so forth. That is, simply performing the motions of the Prayer in the most minimal fashion is not what is desired from us - but rather we should exert ourselves in this affair, bearing in mind that the Prayer is the first matter that will be judged on the Day of Resurrection - if it is accepted then the rest of our actions will be accepted, and if it is rejected then the rest of our actions will also be rejected. Summary That Islam is indeed built on the five principles of: 1) Witnessing that Allah is our only deity and Muhammad (pbuh) is His Messenger to show us how to fulfill our existence on this earth as Muslims, 2) Prayer, 3) Zakah, 4) Fasting and 5) Hajj So one must strive to fulfill these pillars with the utmost care, concern and priority, and one must do so normally before one gets involved with other aspects of the Deen.