Paul was writing from a Roman prison, shackled to chains (Colossians 4:3).  He is writing to congregations he did not personally know (Colossae, Hierapolis and Laodicea – Colossians 4:13) but he knew of their faith from Epaphras (Colossians 4:12) who was a fellow prisoner for the sake of Jesus (Philemon 1:23).  Their work was to pray for the churches, which they did in great detail and with much energy (Colossians 1:3-13; Colossians 4:12).  

Prayer is hard work and for Paul was a part of his agonising labour (Colossians 1:29).  He is not ashamed of his personal struggling as a servant of the gospel.  Everything which is worthwhile will involve some kind of suffering (the word used here is 'agona').  Examinations, athletics, construction and school teaching - they all have rewards when done excellently, but they will all involve struggle and suffering.  Much time is sacrificed, skills are painfully refined, outcomes are clarified, strategies are devised, problems are anticipated; and everything is committed to the task irrespective of the cost - because the outcome is important.
 
Gospel ministry has added dimensions because it is a spiritual battle (Ephesians 6:12).  Although it is ultimately God's work, He uses our bodies, hearts and minds ... which will take the strain and pain.  In addition, even Paul was struggling with his old sinful nature (Romans 7:14-25): he was conscious of Satan's attacks (2 Corinthians 2:11), his missionary travels brought him into conflict with people and exposure to many dangers (2 Corinthians 11:23-29): his prayers for the believers were intense and draining (Colossians 1:9): and he accepted that suffering was a normal part of authentic faith in Jesus Christ (Philippians 1:29-30).  But why did he advertise his struggling?  He wanted them to understand that the sufferings of Christ were so valuable that any struggle in making Him known is supremely worthwhile (Romans 1:16).
 
Neither our struggles nor our prayers can ever atone for our sins or the sins of those we minister to.  They are the privileged mark of those who share in God's family business.  However, many Christians prefer the easy lifestyle options offered by the world, embraced by the flesh and orchestrated by the devil.  For them the 'hope of glory' (Colossians 1:27) is an insurance policy, but their primary commitment is to themselves and their principal objective is pleasure (or at least, the absence of pain).  Every other legitimate call on their time and energy (family, work, money) is given priority above serving Christ.  But wherever sacrifice is real, service for Christ becomes genuine: and the value of the cross becomes transparently wonderful.  So, you see, your spiritual priorities are directly measured by your willingness to sacrifice yourself for them. It is time to assess what should really matter!