In theory Christadelphians believe we are saved by grace, but in practice there is an emphasis on "working out our salvation" through attendance at meetings and Bible Schools, doing the daily Bible readings, and, perhaps more importantly, having "correct doctrine". Someone who errs from the accepted "first principles", even in a minor detail, is at risk of being disciplined at least and disfellowshipped at worst. The details are so important that Christadelphians in North America have been divided for 100 years over whether to use the Birmingham Statement of Faith, or the Birmingham amended Statement of Faith as their basis of fellowship. Most Christadelphians on both sides of the divide would believe almost exactly the same about the "fundamentals" but they cross their "t"s and dot their "i"s differently and so refuse to break bread with each other.
In Australia there have been disfellowships of whole ecclesias (and groups of ecclesias) over doctrinal differences which are too complex for the average Christadelphian to understand. This is the result of placing enormous importance on getting "essential doctrines" exactly right. Getting it right is a "work", and Christadelphians generally believe that you cannot be saved if you get the fundamental doctrines wrong. Taken to its logical conclusion, to many Christadelphians "right doctrine" is more important than "right behaviour" - so we have the absurdity where prominent teachers who are guilty of child abuse, adultery, and unChristian behaviour have been allowed to remain in fellowship while people who are found to have divergent views even on minor matters have been expelled from their ecclesia.
Consequently when Christadelphians discover the truth that we are really saved by grace it is usually a life-changing revelation. God saves us because He loves us, not because we have "correct doctrine". It is the Father's pleasure to give us the Kingdom (Luke 12:32). We don't earn salvation through understanding doctrines. We don't merit any favours because we have a better intellectual grasp of "the Truth" than others. God gives salvation to whoever He pleases. It is a gift - a totally undeserved, unmerited gift.
Once we grasp this truth a huge burden is lifted from our shoulders. We are free to "grow in grace and knowledge" (2 Peter 3:18), to change our ideas as God reveals new things to us. We don't have to struggle alone to be "acceptable" to God - instead He empowers and enables us by His grace to keep us from falling and to present us before his glorious presence without fault and with great joy (Jude 24).
That's why the good news of the Kingdom is the same as the Gospel of Grace - it is by His grace that He gives us the kingdom, not by our own efforts or correct understanding or right doctrine.