Or HaChaim on Exodus 16:4/אור החיים על שמות ט״ז:ד׳

1 ויאמר ה׳ אל משה הנני ממטיר לכם לחם מן השמים, G'd said to Moses: "I am about to cause bread to rain down for you from heaven." It is interesting that in this instance G'd did not instruct Moses to tell the people the news by saying לאמור. It is also interesting that whereas G'd started out by addressing Moses directly, He ended by referring to the people in the third person, i.e. to "find out if the people will walk in My ways or not." We can best explain this on the basis of Yuma 75 that the manna fell for the righteous in front of his tent so that the צדיק did not have to trouble himself to go outside the camp to collect it, whereas the manna for the majority of the people fell in a single area outside the camp and they went outside in order to collect it. The words: "here I shall cause it to rain down for you," were addressed to the righteous, whereas for the people who had displayed a lack of faith the manna fell outside the camp so that they experienced some effort in collecting it.

2The reason that G'd did not preface the prophecy with the customary לאמור was because G'd would command them once more with all the details concerning the manna in the paragraph following. This is why at this moment G'd simply provided Moses with an answer to the people's request, whereas in verse eleven G'd tells Moses to address the people concerning both their demands for bread and meat. The glory of G'd appeared immediately after Moses told the people what was about to happen.

3למען אנסנו, "in order that I may prove them, etc." The heavenly bread required no further preparation by the people to make it fit to eat. This would allow them unlimited time to study G'd's laws. Having this time at their disposal they could show G'd if they would put it to good use.

4Another meaning of the word "I will test them," is the fact that they would only receive a day's supply at a time, דבר יום ביומו; in this way they would remain dependent on G'd's goodwill on a daily basis.