"Be not carried away with divers and strange doctrines. For it is a good thing that the heart be established with grace; not with meats, which have not profited them that have been occupied therein." (Hebrews 13:9 KJV)
"Dear brothers and sisters, if another believer is overcome by some sin, you who are godly should gently and humbly help that person back onto the right path. And be careful not to fall into the same temptation yourself. Share each other's burdens, and in this way obey the law of Christ. If you think you are too important to help someone, you are only fooling yourself, you are not that important." (Galatians 6:1-3 NLT)
This is pretty much the answer to the "heart be established with grace," which if you know anything about grace, it is getting that which you do not deserve; yet in this case, it is our responsibility to give grace to those who might not deserve it, just as Christ has given to us, amazing grace! This is pretty much the follow-through to having mercy, which is usually giving forgiveness to someone; making forgiveness a reason that you establish grace, showing that you really mean that you forgive.
In this Scripture from Galation's, Paul is mentioning, "the law of Christ," which we all should know is that of love towards one another! Love is not something you just say, but it is an action; something that in done, regardless of how you might feel, but because you should know it is the right thing to do!
Maybe I might have not made it clear enough for some, who might not agree with our role in actually showing what grace looks like; because it is actually an action, meaning if it doesn't perform, then it doesn't count! The same is with mercy, as in giving mercy is almost the opposite, meaning that you do not give something that is deserved; like a punch in the nose!
Sorry for that punch in the nose thing, I was just reminding myself of my actions growing up; if was not happy with someone's attitude or denial of my request, then I would just punch them in the nose, making my point that I didn't give grace to anyone, only mercy; and even then, only if they deserved it. You must know, growing up, I had a no desire to respect anyone, but myself; and even then, I didn't really respect my body; if you know what I mean.
Anywho, enough with the strange, "doctrine"; which actually means, "That which is taught," because we are what we eat; meaning, "garbage in, garbage out"; as the story goes...
"Pay careful attention to your own work, for then you will get the satisfaction of a job well done, and you won't need to compare yourself to anyone else. For we are each responsible for our own conduct. Those who are taught the word of God should provide for their teachers, sharing all good things with them. Don't be misled - you cannot mock the justice of God. You will always harvest what you plant. Those who live only to satisfy their own sinful nature will harvest decay and death from that sinful nature. But those who live to please the Spirit will harvest everlasting life from the Spirit. So let's not get tired of doing what is good. At just the right time we will reap a harvest of blessing if we don't give up. Therefore, whenever we have the opportunity, we should do good to everyone - especially to those in the family of faith." (Galatians 6:4-10 NLT)