I don't think that he found following the law to be strenuous, but rather it brought rest for his soul:
Jeremiah 6:16-19 Thus says the Lord: “Stand by the roads, and look, and ask for the ancient paths, where the good way is; and walk in it, and find rest for your souls. But they said, ‘We will not walk in it.’ 17 I set watchmen over you, saying, ‘Pay attention to the sound of the trumpet!’ But they said, ‘We will not pay attention.’ 18 Therefore hear, O nations, and know, O congregation, what will happen to them. 19 Hear, O earth; behold, I am bringing disaster upon this people, the fruit of their devices, because they have not paid attention to my words; and as for my law, they have rejected it.
Matthew 11:28-30 Come to me, all who labor and are heavy laden, and I will give you rest. 29 Take my yoke upon you, and learn from me, for I am gentle and lowly in heart, and you will find rest for your souls. 30 For my yoke is easy, and my burden is light.”
1 John 5:3 For this is the love of God, that we keep his commandments. And his commandments are not burdensome.
Deuteronomy 30:11-14 “For this commandment that I command you today is not too hard for you, neither is it far off. 12 It is not in heaven, that you should say, ‘Who will ascend to heaven for us and bring it to us, that we may hear it and do it?’ 13 Neither is it beyond the sea, that you should say, ‘Who will go over the sea for us and bring it to us, that we may hear it and do it?’ 14 But the word is very near you. It is in your mouth and in your heart, so that you can do it.
