tasu-in that; avatsit-resided; sva-own; srstasu-in the matter of creation; sahasram-one thousand; parivatsaran-years of His measurement; tena-for that reason; narayanah-the Personality of Godhead named Narayana; nama-name; yat-because; apah-water; purusa-udbhavah-emanated from the Supreme Person.