The Maharal makes a comparison between the ברית בין הבתרים, when Avraham was put in a deep sleep, and the four promises of redemption.
Avraham is told that his children will be strangers in a land that does not belong to them. And they will be enslaved and they will be afflicted and afterwards they will go out with great wealth.
The Maharal suggests that we learn the various stages of servitude. The first level is that we are strangers and we don't feel the same sense of belonging as the residents. We realize that this is not really our land. Slowly, we are asked to do acts of hard labor. This labor increases to the point where we are afflicted or tortured until our prayers for redemption are answered.
Each promise of redemption removes us from each level of affliction. It comes out that והוצאתי, והצלתי, וגאלתי, ולקחתי correspond to these levels.
The Maharal further suggests that there are hints to future exiles that began without too much pain, but got progressively worse.
If we would only learn the lessons of history, we would not repeat the same mistakes.