It was taught in a baraita Abraham instituted the morning prayer, as it is stated "And Abraham rose early in the morning to the place where he had stood before the Lord" (Genesis 19:27), …

Isaac instituted the afternoon prayer, as it is stated: "And Isaac went out to converse [lasuaḥ] in the field toward evening" (Genesis 24:63)...

Jacob instituted the evening prayer, as it is stated: "And he encountered [vayifga] the place and he slept there for the sun had set" (Genesis 28:11). …

Avraham prayed in the morning, Yitzchak prayed in the evening, and Yaakov prayed at night. According to one opinion in the Gemara, the three tefillot that we pray today are parrallel to the tefillot of Avraham Yitzchak and Yaakov.

If we look slightly deeper, we find that these three tefillot are three models of turning towards God.

"Avraham arose in the morning to the place where he stood before God" - this event happened when Avraham beseeched God to spare the lives of the inhabitants of Sodom. Avraham turned to God in a time of need.

"Yitzchak went לָשׂוּחַ in the field toward evening" - what was his impetus to turn to God at that instant? There is no indication that there was anything wrong, any crisis for which to ask for God's intercession. This is another form of tefilla - turning to God not in crisis, but as a simple act of living. It is quite fitting that the Mincha tefilla, in the middle of the day, is parallel to the tefilla of Yitzchak.

"And he encountered [vayifga] the place…", this is when Yaakov flees from Eisav. The time is night, and Yaakov is about to embark on a journey in which everything might go right, but it also might not. In fact, Yaakov got quite a mixed bag of things that went right and things that did not. Yaakov's tefilla is Maariv, of hope in the night and trust in God. It is specifically during Maariv that we say "אמת ואמונה", "True and trustworthy", since it is then that we are showing our trust in God.

These three models of tefilla are all integral to our service of God. That is why Chazal instituted all of them - tefillot in times of crisis, as part of living a life of Avodat HaShem, and as an act of hope. 

Shabbat Shalom, 

Rabbi Moshe Abrams