the meaning is that when he intended to come to you he made you a means of attaining his need and a vehicle to attain his love. if it were not for some of the speech you would have a right over him that requires thanks. so thanks are not due to someone like that even if you benefit from that from him if he has done something for himself. because if that benefit had been available to him in someone other than you he would not have crossed over to you.
المعنى في سواك لما قصد إليك، فإنما جعلك معبرا لدرك حاجته، ومركبا لبلوغ محبته. ولولا بعض القول لوجب لك الحق عليه حق يجب به الشكر. فليس يجب لمن كان كذلك شكر، وإن انتفعت بذلك منه، إذا كان لنفسه عمل. لأنه لو تهيأ له ذلك النفع في غيرك، لما تخطاه اليك.