This chapter follows the events of the last chapter, but we do not know how much time has passed since then. Last we knew Yitzkhak was approximately two or three years old. The next time marker is in the next chapter, and there it is written that Sarah was 127 years old. So, if Avraham was 100 years when he birthed Yitzkhak and Avraham was born in the year 1948 after Creation, then Avraham was 102 or 103 when Yitzkhak was weaned, and right after the accounts in the last chapter, the year would have been 2050 or 2051. Avraham was 100 when Yitzkhak was born, which puts us in the year 2048, and Sarah was 90 years old in this year. We know Sarah is 127 years old in the next chapter, so the year is 2085. That means these accounts occurred between the years 2050 and 2085, a 35-year time gap. So, Yitzkhak was between 2 and 35 years old during the events of this chapter. This is important for me to know. I know I made this confusing, but bear with me.

Then this verse reads, “The ELOHIM (meaning the POWERS), said towards Avraham”, which means that YHVH and all his celestial hosts were going to test Avraham. Remember that Avraham is forging his own way now, making his own decisions. ELOHIM is no longer guiding Avraham. Avraham is acting according to the way that he has learned from ELOHIM, meaning YHVH, the messengers of YHVH, and the spirits. He has learn all he needs to know in the way of YHVH or from ELOHIM/POWERS/GODS. Avraham is a full-fledged Prophet now, a man of the Highest POWER/GOD, YHVH, he can also be called ELOHIM, because he was on earth representing YHVH. And now he is to be tested.

Some people may think that this ELOHIM was satan, but I do not think so. Why? Because in verse 16, it says that all of this YHVH did it, and we will get to that soon.

Rashi (approximately 1040 - approximately 1105) commentary:

הנני HERE AM I — Such is the answer of the pious: it is an expression of meekness and readiness (Midrash Tanchuma, Vayera 22).

Ibn Ezra (approximately 1089 - 1092 to approximately 1164 - 1167) commentary:

THAT GOD DID PROVE ABRAHAM. Some say that the word nissah (did prove, tested) is a variation of nissa (lifted up), with the sin replacing the samekh and the heh replacing the alef. However, the plain meaning of the entire chapter contradicts this interpretation. The word nissah is thus to be taken literally. The philosophers teach that there are two kinds of knowledge: knowledge of events prior to their occurrence and knowledge of what is presently in existence. The latter is the meaning of God did prove, and for now I know (v. 12). Saadiah Gaon says that did prove means that God tested Abraham to demonstrate his piety to mankind; furthermore, he interprets for now I know that thou art a God-fearing man (v. 12) to mean that now I have made known to all that thou art a God-fearing man.

The meaning of for now I know that (v. 12) is the same as and if not, I will know (Gen. 18:21). I will also explain, if God, who knows all hidden things, will help me, the secret meaning of this term in my comments on I know thee by name (Ex. 33:12).

Ramban (1194-1270) commentary:

AND G-D TRIED ABRAHAM. The matter of “trial,” in my opinion, is as follows: Since a man’s deeds are at his absolute free command, to perform them or not to perform them at his will, on the part of one who is tried, it is called “a trial.” But on the part of the One, blessed be He, who tries the person, it is a command that the one being tested should bring forth the matter from the potential into actuality so that he may be rewarded for a good deed, not for a good thought alone.
Know further that God tests the righteous, for knowing that the righteous will do His will, He desires to make them even more upright, and so He commands them to undertake a test. However, He does not try the wicked, who would not obey. Thus, all trials in the Torah are for the good of the one who is being tried.

Sforno (approximately 1470/1475-1549) commentary:

נסה את אברהם, to demonstrate that Avraham’s love for G’d as well as his fear of G’d was not merely potential but actual, much as G’d's goodness is not simply potential but actual. The purpose of man’s existence is to emulate the virtues of G’d, and by means of this “test,” Avraham had an opportunity to demonstrate this. When G’d created man, He had set Himself the objective of “let us make man in Our image, etc.,” i.e., as much like Divine beings as is it possible for a creature to be . (Genesis 1:26)

Bekhor Shor (12th century) commentary:

God tested Avraham: He brought him to a test, such that the Accuser (Satan), the prosecutor and the litigator could not say about him, "Does Avraham fear for nothing; did He not protect him and protect everything he has; and even the kings make a pact with him" - in the way that he said [it] about Iyov (Job 1:9-10). So He requested something from him that was more beloved to him than his body and his money.

Ok, I must explain this commentary because of the word used, “Satan”. I explained this before, but Satan means "adversary," "opponent," or "accuser". What it all means is that all ELOHIM is conducting this test, meaning all the celestial beings, which include YHVH, his messengers (angels), and spirits. As we see in the book of Job, in the heavenly court, some messengers serve as the defendant's representatives and the prosecutors. The prosecutor is always calling Satan, not meaning that this is a specific angel, but that he is the one against the defendant, meaning Avraham, in this case. This test is something serious.

Or HaChaim (approximately 1696 - 1743) commentary:

ויהי אחר הדברים האלה. It was after these events. The events referred to are Abraham's various adventures, the torturous route to becoming Yitzkhak’s father at an advanced age. In the meantime, Yitzkhak had grown up since we find Abraham described as "living in the land of the Philistines for many years," and Yitzkhak was born during the first year of Abraham's stay there. The test assumed much greater impact in view of the repeated promises G'd had made to Abraham concerning Yitzkhak and his future.

והאלוקים נסה את אברהם. G'd tested Abraham. The Torah adds the conjunctive letter ו before the word אלוקים to remind us that this was not Abraham's only test, only the most recent and most difficult one.

ויאמר אליו אברהם. He said to him: "Abraham." This introductory call by G'd was to prepare Abraham that G'd would ask him to do something difficult. Abraham understood this; this is why he said, "I am ready (for whatever You are going to tell me to do)."

Radak (1160-1235) commentary:

It is very difficult to explain the matter of G’d’s “testing” someone, seeing that G’d knows in advance what the result of such a test is going to be. What then is the point of such a test? If the point was to demonstrate to the world at large that Avraham successfully passed such a test. The truth is that the purpose of the trial was to demonstrate to the world Avraham’s love for G’d. It was not meant to demonstrate anything to the generation during which Avraham lived, but to prove this to subsequent generations of people who believed in the Torah, which was handed down to us by Moses at the command of G’d Himself. All that is written in the Torah [including such stories as that of Bileam and Balak, none of which had been witnessed by any Jew alive at that time, Ed.] is meant to teach the extent to which we are expected to demonstrate our love for G’d if and when the occasion arises.

Steinsaltz (1937-2020) commentary:

It was not long after these previous matters; God tested Abraham. This is the first event explicitly described as a test planned by God. And God said to him: Abraham; and he said: Here I am. Abraham’s response indicates not only that he has heard God’s call but that he is ready to receive His command.