Why is nothing forced on Christians if they are under grace and not under law?
Grace is not law, so since believers are under grace and not under law, nothing is forced upon them. All of God's grace is experienced at salvation, but growth continues from that position in grace. Believers grow in grace rather than being coerced by law, and that is the beauty of grace.
Les explains that the Corinthians were saved out of abject paganism, idolatry, and immorality, so they needed a time of nurturing and growth, but only by the grace of God. Every person saved by grace experiences all of God's grace at salvation, yet still has a long way to go in growth. Peter's epistle says to grow in grace; believers do not grow into grace. All of God's grace has been poured out the moment we believe, and from that position in grace we grow. Because grace is not law, and we are under grace rather than law, nothing is forced upon us; that is the beauty of grace.