There are few questions that trouble believers - especially young believers - more than how we can know what God's will is. What does he want us to do? Almost the primary discipleship question is "what is God teaching me from the Bible and what am I going to do about it?" Inevitably the first part can be a lot easier than the second part. And yet, doing the will of God isn't just an adjunct. It is pretty much the whole point. God wants us to live with him and to be involved in the things he is doing.

So how do we know? The answer is given in a general principle in Colossians 1:9, where we find Paul praying that God will fill them with the knowledge of his will through giving them spiritual wisdom and understanding. We know his will because God reveals it.

A critical question is to whom does God reveal his will and under what circumstances? In 1:3-8 we discovered that the Colossians:

Had recieved the message of grace in all its truth. They had embraced the truth and grace of God in the good news about Jesus
Had been convinced of secure inheritance that God is keeping in Heaven for believers
Were producing evidence of this work, produced in them by the Holy Spirit, of public faith in the Lord Jesus and love for all the believers

The gospel was working. They didn't just believe but then produce no fruit. Neither were they producing fruit without the foundation of gospel hope. No, gospel hope was being used by the Spirit to produce gospel fruit. And therefore Paul says in v9 "ever since we heard about you we haven't stopped praying that God will reveal his will to you."

Or, in other words, we can confidently expect that God will reveal his will through spiritual wisdom and understanding to people who are living in the three points above. "I have heard God has done this in you, therefore I pray with confidence for knowledge of his will for you."

You can't pray with confidence that God will show his will to those who haven't embraced his grace and his hope, who aren't evidencing it in faith and love. That is the general principle. Neither can you say "I think the will of God might be as follows" if you disconnect it from the Bible, the message of grace in all its truth. If you want to know the will of God, you have to embrace the gospel of God.

1:10-11 then give ... examples of what it will look like when God reveals his will, giving wisdom and understanding so we live a life worthy of the Lord that pleases him:

we bear fruit in every good work
we grow in knowledge of God
we are strengthened with all power by his glorious might so that we can have great endurance and patience
we are joyfully thankful to the Father for qualifying us to share in the inheritance

Then he finishes in v13-14 with praise for how the Father qualified us: by rescuing us from the dominion of darkness, bringing us into the kingdom of the son he loves, redeeming and forgiving the sins of those who are in Jesus.

How do we know the will of God? Basically by embracing the biblical gospel of his grace and asking for wisdom and understanding from God about how to live it out. His will is not just that we understand the gospel, but it is never anything other than living out the gospel of grace in the circumstances in which we find currently ourselves - or into which he directs us to move next.