Quoting Commentary for I Samuel 6:1

והאלוקים נסה את אברהם, G’d now subjected Avraham to a painful test, something which was bound to cause him grief. Whenever the root נסה occurs, such as in Job 4,2 or Exodus 17,7 or Psalms 26,2 the connotation is an unpleasant one for the one being subjected to it. In this instance, G’d, so to speak, indicated to Avraham that he had been foolish to think that he could guarantee’s Yitzchok’s and his descendants well being into the future, as he might have to terminate his life before he even had produced any offspring who would be called upon to honour his father’s deal with Avimelech. We find that the ark of the covenant spent seven months in Philistine captivity as a result of Avraham having made such an unauthorised pact with Avimelech (Samuel I 6,1). The seven months corresponded to the seven sheep Avraham had gratuitously given to Avimelech. G’d swore that as a result the Philistines would fight seven wars against the Israelites in which they would be victorious. These wars occurred during the time of Shimshon, Chofni, Pinchos, Sha-ul, and the three sons of Sha-ul who were killed. Another approach: as a result of Avraham’s high-handed act seven altars (public altars equivalent of temples) were destroyed by the enemies of the Jewish people after they entered the Holy Land Land, They were: Moses’ Tabernacle, Gilgal, Nov, Shiloh, Givon and the two Temples in Jesrusalem. (copied from Midrash Shemuel by the editor of Rash’bam) According to still another version G’d’s ark would repose in the land of the Philistines for 7 months.

I have already mentioned in connection with Exodus 16,32 that the Ark constructed by Betzalel was secreted inside the Temple (of Solomon) together with the bottle of manna and certain other sacred vessels at the instruction of King Yoshiah who hid them under an area of the Sanctuary known as מחילה. There was a special reason why these specific vessels were selected for hiding rather than others. The reason that King Yoshiah hid the Ark rather than most other sacred vessels was twofold; one reason was its superior holy status unmatched by other sacred vessels. Seeing that it was the first of the holy vessels to be constructed, its holiness was greater than the vessels fashioned later. It was perceived as a symbol of the celestial throne. As a result of such considerations it was feared that loss of the Ark would be equivalent to a departure of G’d’s presence from the land of Israel. The king knew that the state of Israel was going to be destroyed by Nevuchadnezzar as the prophets of his time had been threatening this if the people did not return to G’d wholeheartedly. It was clear to him that the conquerors would capture and take with them the holy vessels of the Temple to Babylon; this is why he was so concerned with the honour of the Holy Ark that he preferred to bury it and hide it.
The second reason was that the Holy Ark symbolized for him the journeys of the Jewish people. He experienced that the staves of the Holy Ark which protruded a long distance beyond either corner to enable it to be carried. [It was very heavy due to the outer and inner layer of solid gold plus the weight of the Stone Tablets. I have seen a calculation of the total weight of the Ark complete with contents in Eliyahu Ki Tov’s commentary on Parshat Terumah or Tetzaveh. If my memory does not deceive me the weight approximated 3 tons. (76,000 lbs) Ed.]
During the reign of King Yoshiah these staves became visibly shorter, making transportation by means of them impossible. They reverted to the size they had been in Moses’ time. The king viewed this as a bad omen. Originally, the staves could be seen protruding through the dividing curtain of the Sanctuary from the Holy of Holies by causing the curtain to protrude into the airspace of the Sanctuary where it was pushed by these staves. The retraction in the length of these staves meant for King Yoshiah that the Ark was once more destined to travel, just as in the days of Moses. The Israelites, when looking into the open doors of the Sanctuary, could no longer perceive the curtain bulge at the point they were used to see it do so.
The king also saw that when the High Priest Chilkiyah came to perform the service in the Sanctuary (Kings II 22,8) that he found a Torah scroll on the side of the Holy Ark which had rolled into the Sanctuary instead of remaining in its assigned place in the Holy of Holies on top of the Ark (compare Deut. 31,26 and Talmud Baba Batra 14). These occurrences meant for him that the Temple would be destroyed. This is the reason why Targum Yonathan renders Ezekiel 1,1 “it was in the thirtieth year” as a reference to the year that Chilkiyah found the Torah scroll we mentioned. When considering these various omens King Yoshiah decided to hide the Holy Ark so that it would not have to travel into captivity.
We have established that the sanctity associated with the Ark applied to the Ark made by Betzalel, not the box made by Moses to accommodate the Tablets when he would come down from the mountain many months before the Tabernacle had been erected. Moses’ “ark” was strictly a temporary housing for the Tablets pending the construction of the Tabernacle. Concerning the Ark constructed by Betzalel, the Talmud in Eiruvin 63 taught that whenever the Ark and therefore the Presence of the Shechinah were not in their assigned abodes the Israelites were forbidden to engage in marital relations with their wives. It is totally impossible to understand this statement of the Talmud as applying to the ark made by Moses, i.e. the ark that went to war with the people. Seeing that the Holy Ark was held in captivity by the Philistines for seven months (Samuel I 6,1), we cannot assume that during all this time the people did not practice the commandment to be fruitful and to multiply. [I do not understand the author here. He had previously accused the sons of Eli of taking Betzalel’s Ark to war without G’d’s authorization although normally only Moses’ ark would be taken to war. Moreover, note that in Samuel I 4, it is clear that it was not Moses’ ark the people took to war on that occasion. Ed.]
David is also reported to tell Uriah (Bat Sheva’s first husband) to go home and engage in marital relations, all of this while war was in progress (Samuel II 11,8). Surely the prohibition mentioned in the Talmud could have applied only to the Ark of Betzalel. The lesson the sages taught must have been “When the HOLY ARK was not ‘at home,’ i.e. G’d was not at home, how could the people feel “at home,” by indulging in marital relations and carry on “business as usual!”

And shall remain there forever. Forever in the Levitic sense,³³It can also refer to the fifty year period of Yoveil. i.e., fifty years as it is said, "from the age of fifty he shall retire from the work force."³⁴Bamidbar 8:25. Figuring as follows, we determine that Shmuel's lifetime was fifty-two years: Eili judged Yisroel for forty years.³⁵I Shmuel 4:18. On the day of Chana's prayer he was appointed judge.³⁶Above verse 9. By subtracting the year in which Chana conceived Shmuel, there remain thirty-nine years. Shmuel governed Yisroel from the time of Eili's death for thirteen years, as follows: On the day of Eili's death, the Ark was captured, and it remained in the land of the Philistines for seven months.³⁷Below 6:1. From there, it was brought to and remained in Kiryas Yearim until Dovid brought it up after he had reigned seven years in Chevron over Yehudah, and all of Yisroel had accepted him as their king. And it is written, "From the day the Ark came to rest in Kiryas Yearim, there ensued many days, and they became twenty years."³⁸I Shmuel 7:2. Subtracting from them seven years which Dovid reigned in Chevron discloses that from the time the Ark was captured until Shaul's death, were thirteen years and seven months; and Shmuel died four months before Shaul.