The Gemara in Brachos mentions that a person should connect the prayer G’al Yisroel (that G-d redeemed Israel, which mentions how G-d led us out of slavery in Egypt) to the Shemone Esray. The Rabenu Yona mentions that one of the reasons is because G’al Yisroel reminds us of all of the miracles performed for us in the past and that G-d can repeat all of these great miracles for us. It is to remind us to trust in G-d and to realize His great powers. We should remember G-d’s powers when we say Shemone Esray everyday.