On the third day: that is a long time when it is a trial as great as this. You may have a trial that last for months.
Every time we survive a test, that is an act of worship. Worship isn't just praising God in church, or praying in private devotions, studying his word, honouring him; it's standing in trials by faith. That is a great act of worship, and that is how it is described here. It is also very strengthening to us, and it may well be an act of witness, because others observe that in trial we clearly have a hold on divine resources, and it moves them quite often.
Abraham could not tell Sarah about this. The heaviest trials you and I have to face, and the biggest tests, will probably have to be borne entirely alone, and we may not be able to share them even with somebody very close to us. We may have to protect them from it, and we may have to prove the Lord on our own.