Romans 1:15

So, as much as in me is, I am ready
This explains what he was a debtor to one and another for, namely,

to preach the Gospel;
expresses the readiness of his mind to that work, whatever difficulties lay in his way; and declares what a willing mind he had to preach it also to the Romans, as elsewhere:

to you that are at Rome also;
the metropolis of the Roman empire, a very public place, the seat of Satan, and where was the heat of persecution.