Or HaChaim on Numbers 15:37/אור החיים על במדבר ט״ו:ל״ז

1And the LORD said to Moses: the reason that this passage deviates from the norm in that it says, 'And HE said' whereas in all of scripture it says 'And HE spoke' can be explained by the teaching pf the Sages (Yalkut): When Moses saw the event of the Sabbath woodcutter he said to the LORD, "On the weekdays the Israelites don phylacteries (tefillin) and thereby remember the commandments. On Sabbath, (when it is forbidden to don phylacteries) how are they to remember?" The Holy Blessed ONE responded, "I am hereby giving them the commandment to tie fringes, through which they will remember, etc." This is why "And HE Said" is appropriate. It implies soft words that satisfy the heart of a questioner.