18 The construction is the infinitive construct with the temporal preposition and the suffixed subjective genitive. This temporal clause indicates that the verb in the preceding verse was frequentative.
19 This is another infinitive construct in a temporal clause.
20 In this explanatory verse the verb is a customary imperfect.

In other versions

When they went into the tent of meeting, and when they approached the altar, they washed, as the Lord commanded Moses.

They washed whenever they entered the tent of meeting or approached the altar, as the Lord commanded Moses.

They washed whenever they came to the tent of meeting and approached the altar, just as the Lord had commanded Moses.

Whenever they approached the altar and entered the Tabernacle, they washed themselves, just as the Lord had commanded Moses.

At their going into the tent of assembly and at their approaching the altar, they washed, as Yahweh had commanded Moses.

When they went into the tent of the congregation, and when they came near unto the altar, they washed; as the Lord commanded Moses.

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