22 This is the reason why I have so often been hindered from coming to you. 23 But now, since I no longer have any room for work in these regions, and since I have longed for many years to come to you, 24 I hope to see you in passing as I go to Spain, and to be helped on my journey there by you, once I have enjoyed your company for a while. 25 At present, however, I am going to Jerusalem bringing aid to the saints. 26 For Macedonia and Achaia have been pleased to make some contribution for the poor among the saints at Jerusalem. 27 For they were pleased to do it, and indeed they owe it to them. For if the Gentiles have come to share in their spiritual blessings, they ought also to be of service to them in material blessings. 28 When therefore I have completed this and have delivered to them what has been collected,  I will leave for Spain by way of you. 29 I know that when I come to you I will come in the fullness of the blessing  of Christ.
30 I appeal to you, brothers, by our Lord Jesus Christ and by the love of the Spirit, to strive together with me in your prayers to God on my behalf, 31 that I may be delivered from the unbelievers in Judea, and that my service for Jerusalem may be acceptable to the saints, 32 so that by God's will I may come to you with joy and be refreshed in your company. 33 May the God of peace be with you all. Amen. (Romans 15:22-33 (ESV)
“For they were pleased to do it, and indeed they owe it to them. For if the Gentiles have come to share in their spiritual blessings, they ought also to be of service to them in material blessings.”
The material and spiritual are not so far divorced from each other as we often suppose. The love of Christ is shared in the sharing of material blessings as well as in the forgiveness of sins. So the gentiles share their appreciation for the spiritual blessings they have received by sharing their material blessings with those who sent Paul to them in the first place.
It will be quite a while before Paul makes it to Rome. He knows this. He is going to Jerusalem. He knows the dangers. A person could figure he didn’t really expect to be in Rome for another year at the soonest. So he leaves them with the example of the Acachians that they can gather money over time and share their Spiritual blessings with the brothers to be in Spain, by sharing their material blessings with Paul.