Colossians 1:3 We give thanks to God, the Father of our Lord Jesus Christ, praying always for you, 4 since we heard of your faith in Christ Jesus and the love which you have for all the saints; 5 because of the hope laid up for you in heaven, of which you previously heard in the word of truth, the gospel 6 which has come to you, just as in all the world also it is constantly bearing fruit and increasing, even as it has been doing in you also since the day you heard of it and understood the grace of God in truth; 7 just as you learned it from Epaphras, our beloved fellow bond-servant, who is a faithful servant of Christ on our behalf, 8 and he also informed us of your love in the Spirit.
The text is quite clear that it is not a matter of just hearing the word of truth, the Gospel, which is all about the grace of God in truth. The text tells us that we must not only hear about grace but that we also must understand grace. There is a difference between a spiritual understanding and the understanding that the natural man has. The natural man, regardless of intellectual abilities, simply cannot understand the things of the Spirit of God. Spiritual things require the Holy Spirit to reveal them. To understand spiritual things one must be regenerate which is to say that one must have a spiritual nature as opposed to being born dead regarding spiritual things.
The Holy Spirit will work in the hearts of His people to give them a taste of Christ in His Divine nature and how He is the perfect image of God. Another way to put this is to say that the Spirit works to show forth the glories of God and how He shines forth in the face or Person of Christ. In the context of our present subject, this works out in the Spirit enabling His people to behold the glories of God in the face of Christ and not just seeing this but enabling them to love and to take joy in Him. Yet another angle on this is to say that when this happens the people of God are being made partakers of the Divine nature (II Peter 1:3-5). God is sharing His love for Himself and His joy in Himself as triune with His people. Still another way of looking at this is to say that God brings His people to Himself and gives Himself to them and in partaking of Him because of who He is they are receiving and tasting of grace.
Christ Himself is grace to the people of God. It is Christ joining Himself to His people (and then living in His people) that is what we know of as true grace. It is when the people of God have Christ who is eternal life that people have the life of Christ in them and that is eternal life. This eternal life is given to them by grace alone. This eternal life is the very life of Christ in them because it is Christ who is the life of the believer. God brings His people to partake of Him because of who He is and not because of whom they are or what they have done. This is getting at the true nature of grace.
Understanding grace is to know this grace from the depths of the soul which is part of what it means to love God with all of the heart, mind, soul, and strength. We do not understand grace until we have had it in the whole of our being and we love God as a result of it and know that the love we have for God is from His grace. We do not do any favors for God when we love Him, but instead it is His grace to us in working His love for Himself in us. The love that true believers have for God is in fact a sharing in God’s love for Himself as triune and as such it is only by grace that we love God. If we do not understand that we cannot love God in our own strength, we have no hope of understanding true grace. All that we do should come from love for God, which tells us that all true works are His works in us and so we never work for grace, but instead we work by the strength of grace.
Coming to the understanding of grace requires us to taste of this grace in the soul by experience. Borrowing from Jonathan Edwards, no matter how much we hear honey described and perhaps scientifically explained, a simple taste of honey helps us understand it in a way that all the descriptions of it cannot do. It is by eating solid food that the body is nourished rather than just reading or hearing about food. Mechanics become much better mechanics after they have fixed cars for a few years rather than just having read books about it. A surgeon is a far better surgeon after practicing as a surgeon for years rather than just reading a book about it. In the same way we can only understand grace when after it is revealed to the heart and mind it is lived in us and through us. In this way we practice living by grace when we actually live by grace rather than just hearing about it. A proud person cannot live by grace and as such we must seek and actually obtain true humility by Christ in order to live by true grace. True grace is only understood by those who are truly humble rather than those who just understand the words.