Quoting Commentary for I Samuel 3:3

וידבר ה' אל משה אחרי מות, normally, the expression וידבר in the Holy Tongue is not used to describe specific parts of the verbal message but applies to the entire speech, characterising its nature. This is the reason why we find so many times the word לאמור, i.e. אמירה after the introduction וידבר. This is why verse 2 continues with ויאמר אליו דבר אל אהרן אחיך, He said to him: “say to your brother Aaron,” without a change of subject between the two verses. Seeing that the thrust of the message, i.e. its being connected to the immediately preceding death of the two sons of Aaron, Nadav and Avihu, had not changed, there was no need to once again identity the speaker, i.e. G’d, by adding the words ויאמר אליו, “He said to him,” as is customary in similar constructions in the Torah. However, according to a minority of our sages (Torat Kohanim 1,3) there were two separate addresses by G’d and we would then have to understand the verse as follows: one concerned the prohibition for Aaron not to enter the sanctuary any time he felt like it otherwise he would be courting death. The second time was after Aaron’s sons had died; Aaron was to enter only at G’d’s command. The warning this time was more urgent, warning that G’d’s presence in the sanctuary would be visible from the outside by means of the cloud hovering over the Tabernacle. At that point the voice of G’d addressed itself to Moses again, issuing instructions concerning the conduct of prophets and High priests in future generations. We find a reference to such matters in Samuel I 3,3-4 where Samuel is reported as lying down in the sanctuary of the Lord when G’d called to him.

FOR I APPEAR IN THE CLOUD in this generation to speak to Moshe, but in other generations to call to those prepared for prophecy, as was the case with Shmu'el, as it says (I Sam. 3:3-4), "Shmu'el was sleeping in the temple of Adonai, where the Ark of God was, and Adonai called out to Shmu'el.

When they came to Shiloh, bamot were forbidden. When they came to Shiloh (see Joshua 18:1) the ark was put back into the Tabernacle (see I Samuel 3:3). At this point bamot were again forbidden because at Shiloh the Tabernacle was considered to be at “rest”, a reference to Deuteronomy 12:9, “Because you have not yet come to the resting place, to the inheritance, that the Lord your God is giving you.” “Resting place” is understood to be Shiloh because the Israelites came to Shiloh after fourteen years spent conquering the land of Israel. Once the Tabernacle came to rest in Shiloh, local altars, bamot, were prohibited.