When Eliezer returned with Yitzchok's prospective bride Rivka, they encountered Yitzchok who had just arrived from Be'er Lachai Roi. In Parshas Lech Lecha we read how Hagar fled to Be'er Lachai Roi when she felt persecuted by Sarah, and it was there that four angels appeared to her. The Ramban writes (Bereishis 24, 62) that it is possible that Yitzchok had designated Be'er Lachai Roi as an appropriate place for prayer since the angels had visited that exact site.
We know that angels were quite commonplace in Avrahom's house. This being the case, what was unique about Be'er Lachao Roi that prompted Yitzchok to leave the confines of his home and travel to this site in the desert to pray? To answer this question, Rav Wolbe (Alei Shur vol II pg. 650) cites a Gemara in Meseches Brachos (10a). The Gemara mentions five different ways in which the neshama is similar to Hashem, and among them, "Just as Hashem sees but cannot be seen, so too, the neshama sees but cannot be seen."
The great difficulty in attaining a high level of emunah, can be attributed to the fact that Hashem cannot be seen. When we look out the window, all we perceive is the glamour and glitter of the physical world. Nevertheless, this is all a façade that obstructs our view of "He Who cannot be seen." He sees all that we do, hears all that we speak, knows all that we think, and it is from Him that all bounty and blessings emanate. In truth, the spiritual world is more of a reality than the physical world, and therefore, most of our efforts should be expended with this reality in mind. However, our failure to perceive this spirituality clouds our outlook on life and causes us to digress from the path we were meant to take.
When Hagar fled to the desert and was visited by the angels, she called the Name of Hashem who spoke to her, "You are the G-d of seeing." "Therefore the well was called, 'Be'er Lachai Roi - the Well of the Living One who appeared to Me'" (ibid. 16, 13-14). Yitzchok was accustomed to seeing angels regularly, but that was because he had reached the level were the Shechina rested upon him, and the Shechina is always accompanied by angels. However, the fact that Hagar, a lowly maidservant, was visited by angels was a unique experience. This demonstrated that although one cannot perceive Hashem, He is very much "alive" and involved in the lives of even the lowly and despondent. This was an occurrence that was altogether new for Yitzchok, and this in turn prompted him to designate that site as his place of prayer. There would be no better site to speak to Hashem, than in the very place that He had shown His concern and involvement in the life of a maidservant.
Throughout the generations, the Jewish people have had numerous such revelations: the ten Plagues, the splitting of the sea, and the Giving of the Torah. In the days of the Judges they felt His presence whenever they had sinned and subsequently when they did teshuvah. And throughout the long galus, we too, recognize how He is very "alive" and closely involved in our lives. Had this not been the case, there would be no way our small nation could survive among "seventy wolves." The more we are cognizant of this reality, the easier it will be to believe in, and relate to Hashem. If we succeed in perceiving how Hashem is "alive" in our very lives, our tefillos will gain specialness similar to those tefillos of Yitzchok when he prayed at Be'er Lachai Roi.