Mu'adh ibn Jabal narrated that the Messenger of Allah ﷺ said, "The uppermost level of the matter is Islam, its pillar is salah and the top of its hump is jihad." [Tirmidhi]Salah, we are to understand, is the main pillar of Islam. If you can imagine a tent with five "pillars" or poles--four around the outside, at the corners, and one in the center. That center pole is the one which gives the tent its shape, and that is the salah in Islam. It is the very first obligation on a Muslim after the shahadah, based on a hadith I've related earlier from Mu'adh. It was prescribed in the heavens during the Israa' wal-Mi'raaj, without any intermediaries.
The Salah has a public call, five times a day, to remind the people. This also indicates that we should be mindful of the time, and that the call is made publicly and regularly shows the value of salah--everyone hears it, regardless of where they are or what they are doing. The men and women, young and old, all hear the reminder.
Another indication of the value of salah in Islam is that there is an obligatory state of purification necessary before beginning--wudhu. A person cannot come to prayer unless he or she is ritually pure, having washed after going to the bathroom, being intimate with a spouse, or coming clean from menstruation (for a woman.)
The fact that the obligation of salah remains even if a person is sick or traveling also indicates the importance of salah. There is a hadith to the effect that salah is the best of all deeds of worship. And the first thing we will be held to account for between us and Allah on the Day of Judgment is our salah.