There seems to a great deal going on in Sunday's epistle, you can see my translation below. If we read it ecclesiastically, liturgically and sacramentally it yields much.

My assumption is that Colossians is not just an abstract epistle by which Paul deals with particular problems - as in Galatians and Corinthians for example. But that it is either a baptismal rite and / or baptismal homily - specifically on the occasion of the baptism of Gentile converts. They who were "once alienated" etc. are now reconciled.

We should especially not fear, or explain away, Paul's word about filling up in his flesh what is lacking in the sufferings of Christ? While not explaining it away we should understand it, and explain it to our people. Paul's meaning is the same one he gives in 2 Cor. and Galatians when he glories in his sufferings, and carries about in his flesh the stigmata of Christ -- all of which are the price he paid to bring the gospel to his beloved children. This is in accord with the Lord's word at his ordination: I will show him how many things he must suffer for my sake. (Acts 9:26)

While neither his sufferings, nor ours, are redemptive in the Roman Catholic sense of the word - namely that present suffering (or purgatorial suffering) atones for past. They are redemptive in this sense: that they mortify the flesh. They suppress sin in us by humbling us, and forcing us - if need be - to call upon God for help. Our sufferings also have this effect: they bring us experientially closer to the sufferings of Christ. They help us to better comprehend the great price Jesus paid for our salvation.

A price that is paid in full at the bar of God's justice.

But also a price we must pay every day as we live out our baptism. As we deny ourselves, take up our crosses and follow Jesus to the place of the skull. To Calvary where our "Old Man" is sacramentally crucified with Jesus. But what began there plays out in real time as we struggle with the temptations and suffer the tests that are common to all men.

Today's epistle also connects well with the OT lesson. The promise to Abraham that he would have a son by a miraculous process -- and that all the nations of the earth, the Gentiles as well as the Jews, will be blessed through him. Jesus is that Son of whom Isaac was but an image, a forbear, sign, symbol and prophecy.

While the Jewish / Gentile controversy of the 1st century is not appreciated by Christians today unless they know their Scriptures well, it can be appreciated analogically. This happens when Christians, who are "sons of Abraham by faith in Jesus Christ," comprehend that God loves all of humanity. And, too, that the church by her sacred prayer spreads salvation to the whole world. For the church, in conjunction with Jesus her Head, serves as the world's high priest calling on God to defeat the Evil One, and to keep his promise that all the nations of the earth will be blessed through Christ - then the curse will be over! And what the church prays in her prayers she carries out in real time as God gives opportunity and direction. 

But don't ask how. It is above our pay grade. Know only this. That as Gentiles - those who were not God's people - came to baptism then, they will in all generations. They will because God promised that: all nations would be blessed by Abraham's seed.

Jesus.

Our job is to do what Mary does in Sunday's gospel (Luke 10:38-42). Sit at Jesus feet and listen to his teaching. That is accomplished in holy worship.

(Colossians 1:21-29)

21 And you who were once alienated, possessed of a hostile mind, perpetrators of evil deeds 22 he has now reconciled by the body of his flesh, through death in order to establish you as holy, unblemished and blameless before him; 23 if indeed you continue steadfast and grounded in the faith - and are not moved away from the hope of the gospel which you heard

which was preached to every creature under heaven ...

of which I, Paul, was ordained a minister.

24 Now I rejoice in what I suffer on your behalf, and fill up, in my flesh, what is lacking in the sufferings of Christ for the sake of his Body which is the church, 25 of which I was made a minister by the commission of God, for you - so that the word of God might be fully known to you 26 the hidden mystery of ages and generations ...
But now revealed to his saints / baptized.

27 To them (the saints) God decreed to make known the vast extent of this glorious mystery in the midst of the Gentiles - Christ in you the hope of glory.

28 Him [Christ] we proclaim warning every man and teaching every man with all wisdom in order to present every man Complete, in Christ.

29 It is to this end that I labor, struggling with all the energy that he powerfully displays within me.