Sentence:  Henrietta , however , was at that time engaged in a lengthy correspondence with Joe 's older and more serious brother , Morris , who was just about her own age and whom she had got to know well during trips to Philadelphia with Papa , when he <WSD>substituted</WSD> for Rabbi Jastrow at Rodeph Shalom Temple there during its Rabbi 's absence in Europe . 
Meaning of the word marked with <WSD> tags:  be a substitute