Gal 6

We can divide this final chapter of Galatians as follows:
1-5
6-10
11-16
17-18

Verses 1 to 5
The phrase 'you who are spiritual' connects this section with chapter 5. Those who are spiritual are those who walk by the Spirit, who produce the fruit of the Spirit. Paul is not moving onto another theme or topic, but another part of the same thing.
In passing this is the same word which we find in 1 Cor 12:1, 14:1 where it is usually rendered 'spiritual gifts'. I think the whole section in 1 Cor, chapters 12 to 14 is better understood as being not about spiritual gifts, but about being spiritual. What is the Spirit filled life like? Gal 6 here adds to this picture Paul offers us.

Those who are spiritual bear other's burdens, work for reconciliation. Forgiveness is difficult because we don't want to carry the load which will remove temptation from others, we don't want to engage in the difficult work of reconciliation. What does it mean to say, 'I forgive you, but I don't want anything to do with you'?
Spiritual people recognise their own need for forgiveness, their own need for help with their burdens and learn, in step with the Spirit, what it means to lovingly care for others.