Luke's account is a little more explicit:
37 “But even Moses showed in the burning bush passage that the dead are raised, when he called the Lord ‘the God of Abraham, the God of Isaac, and the God of Jacob.’ 38 For He is not the God of the dead but of the living, for all live to Him.”
-Luke 20:37-38 (NKJV)
While death for the righteous is acknowledged, it is not considered permanent. God doesn't consider them truly dead, for they will be raised up at the last day to live forevermore:
39 “This is the will of the Father who sent Me, that of all He has given Me I should lose nothing, but should raise it up at the last day. 40 And this is the will of Him who sent Me, that everyone who sees the Son and believes in Him may have everlasting life; and I will raise him up at the last day.”
-John 6:39-40 (NKJV)
Jesus said to her [Martha], “I am the resurrection and the life. He who believes in Me, though he may die, he shall live.”
-John 11:25 (NKJV)
God is not the God of the dead, because there is no remembrance of Him in death:
18 For Sheol [the grave] cannot thank You,
Death cannot praise You;
Those who go down to the pit cannot hope for Your truth.
19 The living, the living man, he shall praise You,
As I do this day....
-Isaiah 38:18-19 (NKJV)
For in death there is no remembrance of You;
In the grave [Sheol] who will give You thanks?
-Psalm 6:5 (NKJV)
“What profit is there in my blood,
When I go down to the pit?
Will the dust praise You?
Will it declare Your truth?”
-Psalm 30:9 (NKJV)
10 Will You work wonders for the dead?
Shall the dead arise and praise You? Selah
11 Shall Your lovingkindness be declared in the grave?
Or Your faithfulness in the place of destruction?
-Psalm 88:10-11 (NKJV)
The dead do not praise the Lord,
Nor any who go down into silence.
-Psalm 115:17 (NKJV)
God continued to call Himself the God of Abraham, Isaac, and Jacob long after they had died. This is because, to paraphrase Jesus' words to Martha,
“though they may die, yet shall they live.”