God's covenant with man magnifies the mercy and grace of God. The first paragraph speaks of this infinite gap between God and man. It is a gap that man can never bridge, it's impossible. Though man are to obey and honor God in all things, we could never obtain eternal life by obedience.
Thus, the only way that man could be saved is "by some voluntary condescension on God's part, which he hath been pleased to express by way of covenant." When Adam fell, all of mankind, from Adam and Eve to all of the generations after them, were brought under a curse.
It is only by, referring to the covenant of grace, "the grace of this covenant that all the posterity of fallen Adam that ever were saved did obtain life and blessed immortality." It is important that we understand the covenants which God has voluntarily established. Are you grounded in a biblical understanding of God's covenant? Download the lecture on chapter 7 of the 1689 London Baptist Confessing of Faith.