Colossians 1:5b

the faith and love that spring from the hope stored up for you in heaven and about which you have already heard in the true message of the gospel

(v5, NIV)

What's somewhat sad is that Paul needs to specify with the word "true" when talking about the gospel. Unfortunately, there were a number of false gospels circulating at the time, which is why Paul needed to specify. It is only the true message of the gospel from which comes the hope that brings forth faith and love such as this. The true message of the gospel is all that is really worth anything and we should care and worry about whether we do in fact have the true gospel or not. This true message of the gospel is something they have heard and Paul is encouraging and reminding them of that.