In other words, God's will for us is that we live in the liberty and the joy and the power of full assurance. He means for us to know assuredly that we are bound for heaven and that we will not fail to get there. It is possible for true Christians, with genuine saving faith, to go through periods of time in which they do not have the full assurance of hope. In other words, the heart's true allegiance to Christ and true union with Christ are not completely identical with strong feelings of assurance.
Faith can be real when the feelings of assurance are weak.
But God commands us to be earnest and zealous in our pursuit of full assurance. Because that is where the joy and freedom and power are found. Now there are two ways to pursue assurance. One is by examining ourselves and seeing the evidences that the dominion of sin has been broken and that we have new desires and disciplines. If the fetters of sin be broken off, and we walk at liberty in the ways of God, this is a blessed sign we are pardoned.